I'd imagine this would be fairly simple (and repetitive) plugin to make. Basically what I want it to do is say the price of a thing in the chat. Example: I would type in "/stone" and it would take the files from it's config (it would show in the config "stone = The value of stone is 1 iron coin.) and type out: "The value of stone is 1 iron coin." Could anything like this be made?
There is a feature very similar to this added in Essentials. In the essentials default files, you will find a Prices file. You can edit this to set the prices of items as you wish. Players can look-up prices with a command, and if you allow them the permissions, they can type /sell <item> or /buy <item> to buy/sell the specified item. (I believe the commands are /buy and /sell, if not they do the same thing and are just a different command ) Again, this is all part of the essentials plugin.