most hobby shops sell kit cars that use 2 AA bateries. But if you have to build it from scratch, old walkman tape players have a motor with a rubber belt. You can use plastic bottle caps for wheels, and wire hangers for axels. You can run the axels through straws and loop the belt tight around the axil or put one of the wheels from the walkman in it to make it turn... its up to what ever your imagination can conceive. just a suggestion.