This mod came from a synthesis of two ideas.

• Space travel in vanilla Starfield is inconsequential and, despite all relevant dialogue indicating the opposite, costs absolutely nothing. I wanted to address this without introducing friction to the player experience.
• I love hardcore needs mods. However, I don’t find myself enjoying the interactions as much in a game like Starfield as I do in, say, Fallout. I wanted to strip back what ‘needs’ mods do and create something a bit more abstracted.
  

The solution to both of these was, of course, credits. They are the main way you interact with the game systems, but in the late-game they can become as inconsequential as travel. So, Cost of Spacing simply takes credits from the player when they make port to simulate all of the costs of space travel at once.

A wide variety of factors, such as your ship, skills, port of call, factional allegiances, and more are all taken into account to dynamically determine costs, then you are charged accordingly and can go about your business. This should incentivize thoughtful travel and shipbuilding, as well as more interaction with the game world’s factions and mission systems. It should also be completely seamless and never get in the way of the game experience.

Announcements

Spacefaring Economy has been released. It can be considered an extension of ideas explored here. Check it out if you're looking for a lightweight, compatible economy overhaul that just makes ships and resources make a bit more sense.

How does it work?

The mod consists of a single script. When the player lands in a settlement or enters a properly equipped starstation, all calculations are triggered and ship costs are determined dynamically. The system attempts to withdraw the appropriate amount of credits from the player, with a simple three-strike system handling delinquency in payment.

If it is your first visit to a settlement, costs will not trigger until you exit the ship. Similarly, no costs are incurred at starstations until you enter the station.

How are costs determined?

The port dues are split into three distinct types of cost, a general bonus system, and a maintenance system.
All of these are calculated together each time you land in a settlement.

Costs

Ship Costs scale off of your ship’s size and crew complement. They simulate Fuel, Ammunition, and Provisions, with numerous skill checks.

Port Costs scale off of what location you are visiting. They simulate landing fees, ship services, and even heatleech inspections.

Social Costs are small, flat taxes each city imposes on incoming vessels. They don’t really do anything, of course, you just have to pay them.

Stipends

These are varied and are entirely influenced by player choice, background, and factional allegiance. Not all are positive, so beware!

Constellation Stipend - Captains piloting the Frontier can travel for free on Constellation’s dime below a certain player level. This should smooth out the early game economy considerably.

Jemison Independent Pilot’s Grant - Captains that are unaffiliated with any of the game’s major factions receive a grant from the UC government to offset their travel costs until they have acclimated to the space economy.

Travel Allowances and Stipends - Various factions have set aside budgets to offset travel costs of their pilots. For example, Vanguard pilots can expect a minor reimbursement at any port in the galaxy, or deputy Rangers will see a similar but smaller reimbursement on any visit to Freestar space.

Maintenance

The maintenance system has gone through a few overhauls and is now fully integrated with all other systems. Put simply, travel will slowly accumulate 'wear-and-tear' to simulate systems damage taken from regular use. Whenever you make port or dock with a consumer-facing starstation, there is a chance you will incur a slight cost for maintenance, which will remove some of this simulated damage. Maintenance is performed for free at your Outposts and certain unique starstations.

There are also two 'catastrophic' events that may trigger if wear accumulates past a certain point - Engine Refit and Heatleech Infestation. An Engine Refit is a complete overhaul of ship systems that reduces all damage to 0. Heatleech Infestations run on a separate system and trigger very rarely. Both can be very expensive, but only if you are unlucky. Only one can trigger on a single port call. Notification type is determined by the corresponding Gameplay Option.

Medical Bills are only issued if your ship has hull damage, to simulate possible crew injuries. They will not trigger if your ship has full hull points.

Skill and Ship Checks

These have been integrated into the mod enough to warrant their own section. Most costs, whether flat or dynamic, now check a variety of player skills to determine the outcome. For example, Captains with the Long Hauler background leverage their experience to pay less fees at most ports of call, or those with the Serpent's Embrace trait may find their grav drives with less damage than before after making a jump. Skills are factored in for fuel costs, heatleech growth, port dues, provision costs, and much more.

Additionally, ships from some manufacturers do certain things better and worse than others.

How much does space travel really cost?

Ship Cost calculation is done using a dynamic soft-cap system, with scaling ramping up strongly as ship sizes approach C-class and beyond.
Leveling now has a slight impact on prices - if you can't notice it working, it's working.
Additionally, total costs will scale a bit based on location to simulate local pricing.

Below is a Stronghold landing in Neon - which is already an expensive city for non-locals.

However, a small fighter dropping by the Waggoner farm to refuel and grab some star-veggies can expect to pay a fraction of this.

Somewhere in between, a B-class skiff finds itself in Cydonia with a pilot in desperate need of some Beertinis from the Broken Spear.

Players traveling in the Frontier get all port dues paid by Constellation. You'll see a unique message when this happens.

Starstations and staryards are now fully integrated and perform maintenance for significantly less than terrestrial ports.

And of course, that's all before the reputation system comes into play. The interplay between this system and shipbuilding is the main 'gameplay element' of the mod as your choices directly impact your financial situation - a savvy player with the right connections can still turn a profit running space semis, but make the wrong choices and fail to plan properly and even the Frontier will become burdensome to maintain.

Penalties

I have opted to keep the punishment system simple, so instead of what you might expect from a needs mod - like ship or player debuffs - the mod operates on a three-strike system. Each time you are unable to pay port dues, the outstanding balance is logged and a strike is added. After your third strike, your next landing will incur a bounty of your entire outstanding balance (with slight compounding) with the local authorities. If the local authorities cannot be found, the bounty will default to UC authorities.

No penalty is incurred if you have insufficient funds when docking with a starstation, your ship will simply not have maintenance performed.

Installation

Simply install with your mod organizer of choice and enable the plugin.

If you are installing mid-game, the mod will initialize immediately. 
If you start a new game with the mod enabled, it will trigger once you reach New Atlantis in the tutorial mission.
If either SKK Fast Start or Crimson Start New Game are installed, the mod will start immediately upon new games.

After you see the initialization message, your next landing will begin the mod and it will begin tracking and charging costs.

Uninstallation

If you simply wish to disable the mod this can be done indefinitely by changing the option Cost of Spacing to Disabled and Notifications to Default. The mod will begin running again once re-enabled.

If you wish to uninstall entirely, enter
cgf "_CostOfSpacingScript.COSShutdown"in the console and wait for the message to appear.

Save the game, uninstall the mod, load the game, and save again.

This procedure is not needed for updates. It will revert some leveled lists for safety and is not recommended unless you are about to enter the Unity.

Compatibility

The mod is published as a small master and should be loaded as early as possible.
It is, in theory, compatible with everything.
When used with Landing Animation Reloaded you may be double-charged sometimes.
No vanilla records are touched and all changes are done through the script.

Shattered Space's city locations are detected automatically in the script, with unique mechanics for players with the Serpent's Embrace trait.

Configuration

By design, the mod does not need heavy configuration.
For most players, running the Simulation settings should be perfectly suitable - even with other economy mods.
If you find this too expensive for a casual playthrough, the Streamlined setting is roughly half as expensive.
There is also a Port Dues setting that skips all ship costs if you wish to let other mods like Fuel Consumption Unlocked or Ships Need Gas handle these.
Setting the mod to Disabled simply skips the checks and charges you nothing.

There is now a Notifications setting as well - these are mostly self explanatory. As of 0.90b, certain events will be notifications on Default, but message boxes on Verbose. The default setting will always be the most immersive and least intrusive arrangement for notifications.

Requirements

There are no requirements for the mod to function aside from Starfield updated to at least 1.13.61.

Recommendations

This list will grow as I playtest Cost of Spacing with varying economy mods, but for now it is a list of mods whose implementation I like and that are fully compatible with no caveats.

Build Outpost Items with Credits - This uses similar logic to COS - just take money from me to solve my problems.
Dynamic Repair Bill - COS does not touch any vanilla values, so this synergizes well.
Spacefaring Economy - This can be considered an extension of COS, and is mostly designed around it.

How heavy is the mod?

While this is my first Papyrus mod, I believe it should be very light - the main logic has been changed since release but it still triggers off of vanilla events and is only registered for one or two at a time. It should do nothing at all in the background as all necessary values are stored in Global forms.

Technical jargon below for the curious:

Spoiler:  

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On initialization the mod registers for OnLocationChange, OnShipLanding, OnShipGravJump, and OnShip Dock. 

When OnShipLanding is called, the mod
1. increments the landing counter for maintenance
2. unregisters for OnShipLanding and
3. checks abComplete to decide whether to
A. register OnExitShipInterior
B. call the mod logic (charging the player) and register for OnLocationChange.

Without the OnLocationChange step the logic will trigger on cell change which is tremendously annoying.

When OnShipDock is called, the mod registers for OnExitShipInterior.

When OnExitShipInterior is called, the mod triggers the global logic check, unregisters, and register for OnLocationChange.

Without getting too into it, the global logic is a single function called HandleLandingEvents() which checks ship and player location conditions to determine which calculations to trigger. Currently, ShipLocation.HasKeyword(LocTypeSettlement), ShipLocation.HasKeyword(LocTypeOutpost) and PlayerLocation.HasKeyword(isStarstation) are the main checks, both of which work because of the new OnExitShipInterior trigger.

OnLocationChange checks if akOldLoc != akNewLoc to ensure no double charges are filed and re-registers for OnShipDock or OnShipLanding. Then it all starts again.

OnGravJump just increments on each jump for maintenance.

Planned Features

The mod is nearing a full release, with all core systems offering basic functionality. Below are a few ideas I have for expanding the mod further. Let me know which if any are of interest.

• A lightweight 'wear and tear' system that estimates distance traveled and adds higher periodic maintenance costs.   Done.
• Lore books with in-game guidance on how to influence port costs.    Done.
• Slight inverse scaling for ship costs based on location wealth (to simulate scarcity of fuel and other resources in less developed areas) Done.
• A new scaling method for cargo and passenger delivery quests to more strongly incentivize piloting larger ships. Out of scope.
• A rework of the penalty system with a blacklist from ship services until dues are paid (replacing the current bounty system.)
  

Reputation System Triggers
Note: I would advise learning these organically as you play the game, as some can be pleasant (or unpleasant) surprises.
This information is provided for debugging or extension/patching purposes only.

Spoiler:  

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Jemison Grant: 2700 credits until another stipend is gained or level 35 is reached.
Jemison Grant (NA): 4800 credits in New Atlantis only with equivalent conditions

Vanguard (UC02): 400 credit reimbursement at any port
UC Citizen (UC05): 6400 credit reimbursement, but only in UC space. Vanguard bonus removed

Freestar Ranger (FC02): 600 credit reimbursement in Freestar patrolled space

Ryujin Agent (RI02): 1200 credit reimbursement anywhere. 
Ryujin Agent in Neon: reimbursement quadrupled.
Piloting a Taiyo craft will increase these bonuses by ~50%.

Crimson Fleet Rook (CF02): -3800 credit tribute withdrawn at all ports
Note: If you entered the Fleet via the Vanguard, they will pay a portion of this.
Finished Questline (Fleet): 7500 credit reimbursement at all ports
Finished Questline (SysDef): no tribute

Triggering any of the above except for finishing CF with the Fleet removes the Jemison Grant.

Finished Red Mile: no longer pay the tourist tax at Red Mile

Made an enemy of Zoe Kaminski in the Well: Trade Authority fee quadrupled
Helped Zoe Kaminski in the Well: Trade authority fee halved

Finished UC09: Heat Leech inspection cost tripled, with greater chance of triggering the heat leech event
Also gives discount on the event itself

Background: Long Hauler, Space Scoundrel, Pilgrim: Up to 50% discount on all costs except taxes

Neon Street Rat or Ryujin Agent: No longer pay extortionate 'tourist tax' in Neon

Credits

Bethesda for Starfield and the Creation Kit.
The CK Wiki (and UESP for hosting a clone as it undergoes eternal maintenance.)
Game Maker's Toolkit for an illuminating YouTube video on how video game economies are balanced.
RenamonNonaka's Ash and Adoring Fan for keeping me company in a convenient savegame for testing.
Darkfox127 for a great Scripting with VS Code tutorial (external site link.)
Ceres07 for suggesting a clever way to implement the maintenance tracker system.

Spacefarer - A Modular Overhaul

Most of my mods so far have been designed to work as a modular and compatible vanilla+ series - Hereby dubbed Spacefarer. 
Check them out if you're interested!

Combat
Deadly Effective - Overhauls the blandest vanilla combat perks for playstyle diversity (and fun!)
Balanced Ballistics - Highlights the strengths and weaknesses of various weapon types.
Suit Up - Smart and compatible categorization for vanilla armors.
Space Economy
Cost of Spacing - Simulates a complex space economy by introducing costs to space travel in a lightweight manner.
Spacefaring Economy - Overhauls prices and rewards with heavy scaling to avoid hyperinflation.
Captain’s Choice - Rebalances ship classes and modules for more thoughtful shipbuilding and combat.
Immersion
No More Magic Boost Packs - This is probably my personal favorite. You can’t boost jump unless you are visibly wearing a boost pack.
Immersive Renames [RTFP] - Renames a variety of mod-added items to meet vanilla naming conventions.