I am in Europe so my figures won't apply. I want to strip the car to the bare metal, epoxy prime, and repaint with three coats and then clear coat.
A local dutch guy asked for EUR 10k (about $12k). Another asked for EUR 5k and might be able do a decent job but he takes months. I don't want dutch working on my car because, if I may generalize, they are a nation of pig farmers and fisherman. They have no tradition of craftmanship and it shows.
If the dutch were expensive, the Germans are more so. At least I can be certain of a better job. Still, I don't want to spend EUR 7-8k.
I am looking in Italy. When it comes to craftsmanship, the Italians are the way to go. I have some friends scouting for me in Brescia and Milan. I have been quoted EUR 3.5-4.5k for a complete job. Drop the engine, pull the glass, remove the interior, strip to the base metal, repair rust spots, and repaint engine bay, inside of the car and out with epoxy primer, three coats of pearl and then a clear coat. I think this is the way to go.
Of course I might spend over EUR 1k in gas getting there and back but I could turn it into a mini vacation.
So back to your original question as to how much a paint job for your classic would cost, I can aver with confidence that "it depends."