Once the .8 is established, the .5 will probably be discontinued. Once that happens prices for the .5 will drop and used Pass amps will be a relative bargain in the market considering the sonics, build quality and service.
Prices for new .5 product have not gone up in years. Performance of the .8 product is reportedly better, so they can ask for a price increase, and probably get it. Also, much of this stuff is going to Europe and the Far East where relative prices are even higher.