Some of the more popular/higher production models are listed by NADA. I prefer to search the internet
for old listings etc and try to establish what the last listed price
was when a boat was sold, how the price
moved down over time, or if a boat has been for sale
a long time... and not sold. Comparing all those can give some idea.... but you need to look at the details too. was it a loaded crème puff , or a boat in need of a bunch of work? These details can help you when making an offer too. "This boat is $52k asking... one sold 6 months ago for less than $27k (last listed price) I'm willing to go $32k maybe..."
Brokers are too lazy to figure out the real story.... so use it to your advantage...