Re: US Marine engine
Ya, "might" can get pretty expensive, especially with Force parts geting harder and harder to find, they stopped making that engine years ago and no one makes replacement parts so you are kind of on your own.
Also as Whaler pointed out, check the hull really really well, Bayliners were pretty notorious for having bad transoms and stringers, more the owners falt than the boat but non the less it is 23 years old and lots can go wrong in that time.
Easy way to tell if you should walk is to put your foot on the outboard and slowly get you entire weight on it, if the transom moves more than 1/8'' thank him for his time and walk away.
from the little you told us I would walk unless the boat is REALLY cheap, like a few hundred and that is with a trailer.