Re: 91 Chaparral 1800 SL Limited 3.0
FWIW, I picked up my 1990 2000 SL for $4200. It was repowered with a 350 in 2003, and was under 30 hrs on the powertrain when I got it two years ago... but then I am completely redoing the interior right now..
You can find bigger boats, with more power for less money, but be prepared to put money into them as there really isn't such a thing as a cheap boat, just boat with low selling prices... If the boat you are looking at really is cherry and needs NO maintenance take it to a marina for a full checkout, if they come back with it needs nothing pick her up and have a fun boating season... just don't try to tow anything over 150 lbs unless it is on a tube!
My 2000SL will top 70 with a 23P prop, and jumps on plane with application of throttle, but it does drink more gas than a 3L will, and comes with it's own negatives (cost of maintenance, gas use, weight distribution).
I would have it checked out by the pros, and take it from there!