I have a trailer and do a lot of car hauling for guys around here. In the past couple years I have hauled maybe 20 cars to and from body shops for paint and the prices I have seen here range from $6000 - $14000 for a nice job on an old car or truck. Usually the owner has taken the car apart, stripped it to bare metal, welded in the patch panels and roughed in the body work. The body shop then does the finishing body work to bring it up to their specs and primes and blocks it. I haul the car there in pieces and bring it home in pieces. (shiny pieces) I would say if the car was together and you wanted a "driver" quality job instead of a "show" type job, the prices would be less. Seems like everyone wants perfection nowdays. (myself not included!)
I have a couple of brother-in-laws that work in body shops doing late model insurance work. They make good money doing this and don't even want the problems associated with doing old cars. At one of their shops, if anyone comes in with an old car (older than '80's-'90's) for paint, they tell the customer that their paint jobs start at $10,000 for old cars. If the customer doesn't run away from sticker shock, then they actually will give him an estimate. The estimate usually falls in the $10,000-$15,000 range, but they do beautiful show winning work. Good paint requires even better bodywork and prep and that takes time.