Appropriate price for a Stax SR-007/Mk 1 and SRM-717/Mk 1 system?

Hi, folks.  I want to list the above for sale to upgrade to the SR-009/SRM-007tII (I'm a tube guy at heart), but can't seem to find any history that would guide me to an appropriate price for the pair.  Any thoughts out there on what would be fair?  Thanks!