I have always made a practice of buying valuable numbers matching cars that are in deplorable condition. Then I bring them to my place and do them myself. I have never been upside down in one. Maybe that's just me.....
My first car I restored for me is my Scamp and haven't done another. I had know idea what it would cost when I started.
Bought the best I could figure in parts and think I did the right thing. I haven't had a problem but screwing up my tranny and that was my fault.