If you are planning on working on it yourself and have a little mechanical ability I'd say grab it, and look for another one too. A parts bike can be a valuable asset when rebuilding an old bike. Many parts interchange from year to year 1969 through 1978 on the 750's. I don't think I've ever seen a complete one that wasn't worth $80.
If you would rather have a rider now for more $$ keep looking.