I was thinking of cancelling everyone's money so far, then everyone gets an amount of money extrapolated from their current score. Players would still earn money from races in the same way they do now.
AdrenalineX then sell items (such as wheels, body kit parts) in a /servershop, each one will be given a price relating to how exclusive the item is.
For example the Twist wheels could be targeted to the richest 10% of players, so whatever amount of money the poorest person of the richest 10% of the server has...that would be the price for the item. Prices would of course be recalculated regularly.
Once someone has bought an item they own it outright and can apply it to as many cars they like every race, until they sell it.
If they want, at a later date, players can then sell their owned objects with /sellitem [item name] [amount] and their item would be added to a list /usedshop where other players can buy the item (we could also set fees taken by the server for selling, as a percentage of the sale price or something).
This way we have a steady flow of money both into and out from players' pockets which is based on their performance, giving them a chance to show off how well they play, or how shrewdly they can buy and sell items.