Used Ayre amp market pricing

I find the Ayre nomenclature confusing in that there are models with the same letters and number but their order seems significant.  I'm looking for a VX-5, not VX-5 Twenty, and wonder what the used market price is likely to be.  A 5-VX is too tall to fit in the space I have with 3" clearance.  Any advice will be appreciated.

db