Look at most small cars and the rear plate is possibly 1ft of the ground,I would/will (eventually) put it low down but not too close to the edge of the panel.
Cost : Little as possible.
Thanks : To those who by their generosity my build has progressed.
Its a handmade sports car not a flaming kit car !!!
If at first you dont succeed,avoid skydiving...
No parachute require to freefall,only if you want to do it twice.