Boston Whalers are built by forcing active foam in between the hull and deck structure and then rocking the boat around to make sure there are no voids. The foam provides structural rigidity and floatation. If the boat ever takes a hit and the foam gets waterlogged, the boat is ruined. Try to weight the boat before you buy it.
I bought a 5.2 on a trailer for $5,000 back in 1980, sailed it for five years and sold it for $5,000. In 1995 I saw one in the Jacksonville newspaper for $5,000. They're that good. $3,000 may be reasonable for a 5.2 in good shape.
The Harpoon was a stable, fast,, bulletproof daysailer.