A friend of mine has done 5 or 6 ground up cars the last 10 years.
He takes them down to a shell puts them on his rotisserie and takes them to a shop for body and paint work only.
He gets everything else ready for reassembly while the body is gone.
Everyone of his cars gets the bottom painted.
All of the sheet metal installed and aligned.
On the low side he has spent $8000 on a car that needed no panel replacement to $30000 for one that needed extensive repair.
This Road Runner was on the low side, a rust free California car.