I paint cars...black is a conundrum: it is the cheapest paint to buy, spraying one color versus another is pretty much same-same, but black is picky. PICKY. The surface to be painted has to be perfect, or it will show. Black shows EVERYTHING. How much it would cost depends on the range of the norm for where you live to paint old musclecars, and which particular shop you take it to in your area. Also add in the twist that the bumper covers of 78 T/A's were not made of the same material that non-metallic bumpers are made of today. Even the factory paint only looked good until somebody climbed on the car, or leaned on the car, or looked at the car for too long. The paint had to have plasticizer added or it would crack and craze even quicker. Not soliciting your business, but at my shop a rear bumper re-paint with the proper materials would run about $300-400. But I'm a classic car guy, and I think it's just thievery to charge more to paint a car because it's older or classic. At my shop, it takes no more work, even if you're starting from scratch on a restored car, because I go to the metal/fiberglas/plastic on EVERY paint job I do. I personally have never seen a fifteen thousand dollar paint job. I have seen cars that were painted for fifteen thousand dollars, but they look no better than a car that was properly painted for two thousand dollars, I don't care what ANYONE says.
Shop around. Stay away from any body shop that rolls as many through as the manufacturer--quantity equals profit but not necessarily quality. Look for a guy who's been in business for a long time. Check out cars all over his shop. If it looks shifty or short-cut, it probably is.
Since it's no insurance job, just tell the guy no look-see, no business.
FYI, my work is guaranteed for three years not to fade, peel, or fall off, as long as the customer follows directions about care and feeding. Look for a similar guarantee. A good painter trusts his own work enough for that much. Hope some of this helps.