I have done one ground up restoration project, that I originally estimated would take 3 years to complete. I had the car together and running about 16 years later, and maybe another 2 years before I had some issues fixed, and detailed it enough to enter in OE judging. 3 shops and close to 3 times my original cost estimates by the time it was done.
I don't think I could take on another restoration project as I don't know if I'll live long enough to see it completed......
A related and perhaps even more relevant topic would be asking how many "I'm gonna restore it someday" cars that people see sitting in garages and storage, and even outside, actually ever get restored by their long time owners? In the storage building where my "I'm going to sell it someday" '71 V code Challenger R/T has been stored most of the last 7 years, there is a gator grain top Challenger T/A that has been there for 30 years. I was just thinking about this subject, as a friend of mine asked me to find out if the owner might sell it so he can restore it. I talked to the manager of the building the other day about it, he says many have asked but the owner, who he thinks is in his early 60s now, is adamant he will restore it someday. Cars like that are everywhere it seems. Some outside, and often rotted beyond any hope of restoration by the time the owner finally lets it go. A loaded 71 Challenger R/T 340 and a 70 V code Mr Norms sold Challenger are 2 examples that each were within 5 or 6 miles of my house, sitting outside dying slow deaths.