You might also want to check the BUC Book prices on the boats. In theory, BUC reports actual
sale prices rather than asking prices (Yachtworld) or theoretical "used retail" (NADA) prices.
Then you're still going to need to do some digging, local market conditions, and actual
boat conditions (rarely totally documented) can make a world of difference in real values.
In Practical Sailor's
used boat reviews, they also run
charts showing actual (?) market prices of specific models, across periods of years, in typical condition. That's another option if what you are looing for has been covered in their
reviews.