PAINT Cost?
The only panels on the car requiring extra attention are the two front fenders.
You could have 40 years of surprises under that paint. You are talking hours of disassembly of often rusted and stuck bolts. You have labeling/cataloging of all parts removed (something I would do on a job like this).
Days to remove the old finish.
Days of body work, I don't care what you think, your car isn't straight. I could show you dents and waves that you don't even know are there.
Priming and blocking can take weeks.
For what you asked, disassemble, strip, body work, paint, reassemble, at my shop, you would be looking at $15,000 - $20,000.
If I were to do this as a side job, it would still be $10,000 (+ an additional amount for whatever I find under the paint).