The final number really depends on the shop/individual and what there access is. Either way there not buying new. If there patient and don’t have a line already on a donor when they buy it they’d probably buy the car for mid twenties and a powertrain could be had in the mid to high 20’s You could do that car for 60’s if you know what your doing. What most don’t understand is guys that do this for a living have a lot more access to parts then the average person. There’s many times that donors are floating around that never see the auction or come up for sale to the public. Builds like this are not for the faint of heart with no experience. The builders I use to buy were typically 6-18 months old, clean title, and when they were done the warranties were still in intact. A good shop can repair a car that is virtually indistinguishable from the factory. When I was doing it I had a list of particular cars and trucks people were after. That car would make a great driver and track car for a good price.
I guess it has to be looked at from a couple of different perspectives. If a person/organization has the contact for parts and doing their labor, then probably worth it. For everyone else, it will probably become a very costly purchase.