Trading System
Unending Galaxy uses a relatively straightforward economic system. Factories produce wares out of basic resources that can be found in some sectors of the galaxy (solar energy near suns, various ores in asteroid belts). More advanced factories build finished goods (ship parts, station parts and trading goods) with those wares. Stations lacking resources will buy at a higher price tag than those with an overflow.
The ship and station production capacity of a faction is directly tied to how many ship/station parts it can produce or buy. If a faction is hit in this production chain, either by destroyed transport or factories, it won't be able to replace military ships without spending additional money to import materials from the home-world. And if it has no money left either, military production will be halted.
Factories
Factories produce wares periodically using resources. In Unending Galaxy, they are self sustained, they manage their supply / selling cargo ships automatically. Factories lacking a specific ware may post a mission requesting for such ware at a higher price than usual.
Some low level factories gathering basic resources like the Solar Power Plants don't need resources but can only built in a limited amount in a sector with high amount of luminosity, like near suns. On the other hand, mines (iron and silicium) can only be built on asteroids, and depending on game settings, may deplete after a while.
Trading Stations
Trading stations collect wares produced by factories and act as a trading hub for planetary colonies, they can also act as resource sink if there’s an overflow of a particular product. And, of course, sectors lacking a particular product will buy it for an higher price than sectors having too much of it.
Also, all available trading missions in a given sector are displayed at the trading station. Building a trading station in a sector with a planet allows you to build and control a colony in that sector.
Wares
Unending Galaxy, in its base form (non-modded) won’t feature as many wares as X-Universe games, firstly because I lack graphic assets to have a bazillion factory types, and secondly because I don’t really think it’s needed to have 10 or so variants of the same exact product. More isn’t necessarily better.
Wares are divided into 3 categories: Primary resources, like ores and energy, are directly mined or gathered from the map by the relevant factory. Then, they are moved to other factories producing intermediate resources (like metal allows, microchips) that will then be used to produce trading goods (computers, medicine, food) and ship/station parts.
There's also illegal wares in some territories but not in others. They are mostly produced and traded by the Pirate faction. Dealing in such wares will give you a bigger bang for your buck, but if you get scanned by a police or military ship, your career as a smuggler may be short lived.
Ship Production
While ships can be bought directly from a 3rd party, they are mostly produced via the economic system. My game engine allows for individual ship (or weapon, shield..) production from factories, however this is not the approach I use here. Instead there's “Ship Parts” components that are produced by a relatively long (depends, it can be faction specific) production loop. Those parts, when transferred to a shipyard can then be converted into ships. How many parts are needed is ship dependent (bigger ship = more parts).
This system makes things much easier for the AI to keep ship production running and estimate its military strength accurately. Also it could lead to the implementation of interesting behaviors, like attacks of supply transports to keep an enemy war machine down.