I'll add this, NADA had my boat in a $10k range for the longest time and that was not much lower than MSRP. It was a new tooled boat, but ....... It also showed a $4500 add for a BB which mine came with but now is more like $500. If I go by NADA and include data on the new motor, the add $$ is insane!
It's now adjusted but is still a broad range. A banker type person used the low retail as a wholesale number also..just FYI.
BUC seems to be one of the more respected and a little more accurate. But, accurate is only as accurate as pricing in a specific region can be. Not near as simple as cars especially when it comes to anything not on a manufactures books/custom.