Take a look at
http://www.nadaguides.com/autohome2.aspx? k=1&wSec=10&wPr=0&wPg=2111
to determine what the going price for that rig should be. I'm not aware of any extraordinary issues with that particular engine. Make sure you do your home work on compression check, spark plug condition, water pump, lower unit lub, etc., etc. Check around your area for a reliable outboard shop and have them take a look at it before you write the check.