It don't sound like any sort of speed demon to me.
I'd probably put the likely price of any 1987 boat in that category in the $2500 to $3000 range tops.
Check the exact model with NADA for a current value.
http://www.nadaguides.com/default.as...&y=1987& ml=C
I can't say that I am personally familiar with those Mercruiser motors from those years, but it does sound small for an almost 20' boat.
Take the total weight of the boat into consideration vs. hp rating and compare it to other known boats to get a better idea on how its likely to perform.
It don't sound like anything I'd be too eager to jump on, especially at that price.