Re: I am buying a fiberglass Sport-craft 1973 tri hull . I think its a sportsman 160
I bought mine for $500. Had to get a different engine ($800), new seats ($300), hull work, engine tune-up, fishing seats ($400). That was the 1st year. I'm happy with it cheaper than payments on a new boat and motor. I have a winter projects for the boat this winter. With all of that it's worth the effort; at least if I break down or have problems on the lake I have a clue as to what is wrong. I think the boat you are looking at is worth the $500. Provided it doesn't leak, a good transom and deck. If the engine has problems you can trade it for one that works with some bucks added to the price or buy a used one and part the engine out good used parts still have quite a bit of value.
If you find problems with the boat this site is a good place to go to for advice and how to ideas.