The reason you get such a fluctuation in prices for this item is *it's crap*.
Almost nothing used it. All DVD players now play VCD discs. It really isnt an item that enhances the Amiga experience at all.
HOWEVER, CD32 owners have a longing need to put something in their empty slot :-)
Most cannot afford SX32/Pro etc. so an FMV card fills the gap.
A few years later when the income is flowing they get sold off as people by SX32/Pro or Promodules etc. and need their slot back.
This buy and sell fluctuations means that every now and again several hit the market at the same time and drive the prices down.