yes but compare your rates to say one of a motor builder or panel beater... to build cars can cost you huge amounts of money that you worked for from 9-5.
Doing it yourself is materials only and you get to keep what ever dollars you made earlier that day and at the end of at all you come out on top, yes you did the work but cash is cash!! Especially for some the joy is building the car not so much the driving, maintaining etc..