The core requirement is to have different prices from A to B, to allow the player to make money by transporting goods.
It should be somewhat predictable to the player. In the way that a player can tell from experience "In a system with this and those features, the goods X, Y and Z use to be cheap, goods A,B and C use to be expensive". The question right now is, which features (preferably such that the game already calculates for a system), will influence the prices of goods?
Once this is answered, some dynamics would be good on top. I think it would be very boring for players if the prices never would change. These dynamic changes can be pretty random, I assume, just need some artificial reason like a message when the player enters a system "Newsflash: Big drought ruined this years harvest", and the prices for food skyrocket in this system for the time being.
It doesn't have to be realistic. But it should be believable. I want it as simple as possible, within the bounds sketched above.
Society and technology
I feel uncertain about the influence of government type on prices. At the moment anarchic systems got very high prices for everything, dictatorships high prices and the other government types normal prices.
I'm working on basing most prices on natural resources of the planet in question. I think I have the metals resource based prices done now, and I'm working on mineral based goods.
I don't have a technology level for planets yet, but I assume I need that to determine both, the availability and price of advanced goods.
Prices can change much in between systems, and I'm not quite decided if this is alright or not. In some cases the prices change by a factor of about 10, if one system has abundant resources of something, and the other system has a severe lack of this.
See also: Main Page