^not anymore, $600 id say is what you'll get, 580's are going for $300, heck i put my 580 up here and on cl for $285 and got one stupid offer at $240, so there isnt much demand for a highend last gen used card. Also you got to remember, the people who buy the expensive cards arent really going to buy used unless its a new gen card(from what i've seen and experienced here) that has a substantial discount to warrant the buyer to buy used over new. I mean i have my 6990, for $430 with a block and no one is biting. Honestly i think ill get quite a bit more going the ebay route, and same with you, us hwc guys ill admit it, were cheap.
I personally wouldn't pay more than $450 for one if it has lifetime warranty, and original accessories and packaging. The GTX 680 ($500 on Kijiji) is nearly on par with it with less heat, power consumption, and can actually overclock without the worry of potentially destroying your card.
For the Hydrocopper, I would say between $520-570.