It's certainly true that you need to be clear on WHAT was/is done at the same time you talk about HOW MUCH it cost, as the two go hand in hand.
I could see 20,000 if you drive the car into the shop, and they disassemble it, do all the metal work, prep, undercoat, filler, primer, spray, and reassemble. But that's a very different job from a respray of a car that already has the metal work done, is disassembled, and will be reassembled by the owner (which is what I think you are looking to do). For that 5000 doesn't seem out of line, assuming they do an excellent job.