Forgetting the tool supplies, all of the cost that goes into painting a car is labor. Paint is a very small factor.
Sand, sand, bondo, sand, primer, sand, primer, sand, clean, wipe, mask, wipe, time to paint!
Before painting, I've already got a day's worth of work in the car. A shop would probably charge about $500+ for this alone, plus $100 in sanding paper, bodyfill, and primer. An individual would've spent about $100 in sanding paper, bodyfill, primer, and garage prep, assuming they already had a compressor, an orbital sander, and a mask. The bulk of my cost and labor is already spent. All the car needs is a spray and time to dry.