Early game is fun. There are lots of cool choices to make and one of them is what to do with your money. However is is all too short because pretty quickly you can be rolling in filthy lucre - unless you start an Akan habit in Rigel or something you will generally not want for cash except for a few one time purchases. It's fun to have to sell your fuel for ammo or to pay off your black market debt or whatever. Being rich is curiously enough not that great.
So we thought, what are some things we can do to add more costs for the player? Right now if you don't count upgrades (which more often than not you just find laying around) you have fuel and the occasional armor repair to pay for and even those you can find laying around.
So here are some things which might cost you (an expense is required or constant and a cash sink is optional or one time - there is a bit of overlap between them sometimes)
Docking permit/docking fees - aka parking meters
Membership fees for various things
Fines - for littering, speeding, firing your weapon in an inhabited zone - not all the time but occasionally you may get hit with one, especially if they don't like you. Some stations may be overzealous and fine you basically everytime you pass (for looking at them funny or something)
Item permits - to use items of level X you need the appropriate permit (or a sufficiently well-forged fake permit).
Ship maintenance -
Basically adding a whole bunch of devices like reactors (also we propose the "default" reactor be actually installed, same with default engines, etc).
Note that these can be 0 slot items or use special slots. Most of them need to be maintained.
Every ship has these systems:
Weapons system - this ties all your weapons together and lets you handle basic firing, etc. Governs what type/how many (note ships can still dictate number of weapons)/what level/size of weapons you can install, may provide bonuses, etc. Occasionally needs a repair or maintenance or weapon performance will suffer. (an item could do these maintenances as well as a station service)
Life support - keep you alive, of course. Better life supports could provide protection from radiation or other effects. Must be restocked with food/air every now and then. (again, can be from an item)
Engines - just your drive - we are suggesting that the default be given a device and be replaced when you add a drive enhancement. In addition, occasionally will require some maintenance to change the space oil or whatever.

Reactors - same as now but the default is an item as well and they occasionally need a tuning.
Maneuvering thrusters and targeting computers can also be devices in this vein, with better ones providing better turn rates and aiming services like reticles and etc, respectively.
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more expenses:
Ship loans/leases- ships can't be cheap so you may have to lease a ship or get a loan.
If the black market/anyone is angry at you, instead of paying them outright by docking, it might be more interesting to pay in installments - so you dock sometime (or are forced to dock) and they are waiting for you, demanding the next payment, giving you the opportunity to scramble to pay or run if you want.
If a station destroys a ship that is attacking you it could charge you - this will cut into alternate ways to destroy enemies so we propose the following:
If you are either far enough away or you can trick the enemies into attacking the station instead of you (would require less singleminded enemies) then you are not charged for the service.
Also, since that would require enemies be a little less cautios around stations (right now they won't even think about firing near one) all good from stations are marked and if you try and sell stolen goods that is illegal (can still fence them at the black market though).
I also suggest in a somewhat related idea that corp cruisers be more reckless - if you were in the area, you are guilty too (only counting towards freelance ships, no chain reactions in St K's

Also since this adds a lot of smuggling we suggest being able to be 'pulled
over' and searched.
EDIT: Another idea is leased or rented items.