I've been in the restoration biz for 43 years. In today's market with cars this old there's no way I'd quote a fixed price. If I did you can bet I'd cover my back side with a heavy (worst case) quote, and that way I make proper $$$$$ when it goes south. They usually do go bad once you're hip deep into it. These cars have been in the hands of owners and shops that might not have had the respect for the cars that they deserve. I don't do too many muscle car restorations as I'm quite busy with heavy American Classics like Packards and Duesenbergs. My clients also enjoy something approaching 150 significant and provenance making awards from their respective peers/clubs. The average quality refinish of a well restored and properly fitted muscle car body runs about 180-200 hrs alone. That's block, paint (as a complete assembly in some cases), and full cut and polish, ready for final assembly. If the client wants a truly exact OEM finish (it can be done) that can add another 25-40 hrs depending upon the color/finish. Sheet metal repairs (panel replacement, floors, braces, etc) can't go by any form of "book price" from the past. Most replacement body panels are so far off that clients that I'm used to serving wouldn't accept it at any price. That additional labor to make right isn't on the shop doing the work as it's not us that made those crummy panels, but it's on us to make it right.
At the end of the day you get what you pay for. Some of my work that's over 20 yrs old still scores perfect or nearly perfect (99.5 recently). It's that longevity of the work which is the big intangible value and can only be assured by reputation and, most important, mutual trust. Maybe this helps, maybe not, but going with a known and respected value up front is the best value there is. Value vs price. Which means the most?