My solution doesn't require spawning in money..? My solution listed above is that all cars belong to the current owner that last purchased them In-game, and that they could be purchased by the original donation purchasee within a limited time (like 30 days) for a mandated amount (that is the same for ALL vehicles) and if the original donation purchasee doesn't wish to buy back their car, than going forward cars would be locked to the current item holders at the end of that limited time period.
The refund system is the ability for the current holders to be given a chance to hold onto their cars, and if not be refunded by the original purchasee via refer above mandated amount within a certain time frame before the car plugin is locked in.