HOTRODPAINT and Dave Severson are right. There are just too many variables in prepping and painting to get a reasonable idea of cost here. I did my first complete paint job in 1966 and a gallon of '66 Corvette Nassau Blue acrylic lacquer (DuPont Lucite) cost 12 dollars a gallon. That same gallon of lacquer, if it's not already illegal in your area, will cost well over $200 now. Labor is the real killer in show-quality work, however. To make a finish truly show worthy is very labor-intensive.
Still, $30,000 seems outrageous unless they are taking the car apart, painting every piece, and then reassembling. The next question would be if the car is worth it. Unless that car is unusually rare (like an original Hemi with numbers-matching parts) it's probably not worth $30,000 finished...