To me for some reason it'd make some rational sense that there's some post apocalytpic games (made or going to be made) where the towns might have a different commerce system from each other. While It'd add a lot of variety to the game as you track down different things for money to buy things in the game (not counting trading things), for someone like me making the game I'd probably make a few that are rather offbeat. Imagine being in something like Fallout3 where you go to one town & aside from the standard ideas of money in the game (bottlecaps, pre-war money, guns, ammo, fresh water) I'd probably go with one town using signs as money (great idea until others try to find the town only to get lost without a map) or something else that's abundantly easy to find but massively encumbering (like 200 lb stone discs), rocks or my personal favorite while thinking of this idea: brass instruments. I pictured someone coming out of a wrecked department store with a bunch of stuff, barely able to move with all the loot only to trade stuff away & get rich at this town but their idea of rich is a few tubas or maybe a brass trimmed pipe organ...at that point I'd just go back to whatever town had the stupidest populace & become grand overlord while saying screw these quests forever.