My dream-economy for V13 would be completely anarcho-capitalist.
The only thing NPC vendors would have are very basic things, and they would have only a small amount at a time--nothing like an infinite amount of items (why should NPCs have an infinite amount of items!). And the prices would be based on the going rate taken from player-to-player trade
in that area. You should not be able to sell to an NPC and receive some kind of "global" currency like caps or coins.
When I say "in that area" I really mean that. There should be no global economic trading system whatsoever. I am not opposed to "trading posts" (auction house) in places with a higher population, but you should not be able to trade with someone through a mail system and you should not be able to bid on an item at a trading post you are not currently standing in. And the bidding would consist of people anonymously bidding on something with the seller having the option to accept a bid immediately if he likes what he sees or to wait for the time to expire and choose out of all the offers given...or choose to accept none of them if they all are crap offers!
As far as currency, well that should just develop naturally as the players see fit in each area. If the players in an area, for some reason or another, seem to have developed an economy where they base the value of items on how many cotton balls (or whatever!) they're worth...then so be it. If a player wants to trade a couple shovels he doesn't need for 10 cotton balls, knowing that he can get 20 .45 hollow point rounds for 10 cotton balls from someone else, then he is allowed to do that! The players will naturally make the game if they know ahead of time that there won't be loads of hand-holding.
This leaves room for change, if wanted or needed, and any other kind of natural evolution that goes along with ever-changing factors like: number of regular players in the area, large amount of new trade (or less trade) coming in, a game update that adds tougher raiders in the area who drop better gear, etc.
This kind of system puts even more control into the players' hands over one of the most important factors in the FO world--which is equipment...many times the difference between life and death!
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If you couldn't tell from my older posts, I always focus on economic systems in MMOs. I have yet to find a game that: 1. Makes sense to have this kind of system, and 2. Implements this system in every sense. In my opinion, this is the only type of system that truly makes for V13.
I have a million-and-a-half ideas for V13's economy, trade system, currency, etc. And I look forward to replies and messages!