This is just my opinion, but Yamaha didn't have a decent 750 until 1985 when they came out with the FZ 750. It's five-valve head and canted engine blew everything else away. Your's must be the triple which is a good bike, but... A free bike is great, but it depends on how much work must be done.
I have a 1979 Suzuki GS1000 that I bought new. I debated a long time about putting $350 worth of new shocks on it as the value of the bike is only $1K. But I've had the bike over 26 years and it was Suzuki's superbike at the time. It is now a great handling, classic superbike. Depending on how much time, money, and parts scrounging you have to do, you may wind up with an average, old 750.
Bikes are easier to work on then cars. I would look for a classic bike from the 80's or 90's to fix up. Something that would give fits to someone on a new bike. Some just need modern brakes, tires, and suspension.