I like alot of players went looking for a Bass Whammy only to be turned away by $500-$700 bay pricing.
I bought a used Whammy IV at a music store for $129 and got a few months use out of it before buying a Whammy II $230 buy out.
I could not believe the difference ....the II provides a better tone and tracking (for bass) than the IV does as well as having the foot switchable mode select the IV does not have . I wish had found this information before buying the whammy IV...I could have saved myself a couple bucks.
IB
The Whammy II is a well-kept secret.
It doesn't hold a strong used value because guitarists are nuts about the original Whammy. It may not have the coveted 5th Up / Octave Up of the Bass Whammy, but if you don't need it...