I've seen them go for more than $300, but that was a few years ago. Prices of non-grails or semi-grails (like the 5250) have gone down in my opinion, because Ebay has become saturated with them. Regular people (not us) have discovered that people actually buy these things. So you've got every tom dick and harry slapping theirs on Ebay.
Another example is the RX-5500, one of them sold for $700 about 3-4 years ago

but now they only sell for $150-250.
Same with a GE 3-6035-- I put one on Ebay at least a year ago, I think. I got $300 for it, but the buyer backed out, because some a-hole listed his while mine was still up (and even copied part of my description). Since then, a bunch of other wannbes have tried to sell theirs too, and the resulting over-supply has driven the prices down to $60-80.