I have awesome idea about plugin which enables admins to open stores where will be sell a permissions for players for example Player want to chated with color messages but this pemissions didnt allowed to this player but he can go to shop and buy it for that money that establish admin that can be placed in the signs as chestshop i think this idea will be interesting for yours excuse me about my english i from Belarus
You can use serversigns to sell permissions through a sign http://dev.bukkit.org/server-mods/serversigns/