The prices on these amps seems to fluctuate a lot.
I got mine for $385 on ebay, but the guy didn't tell me that the entire channel switching circuit needed replacing. Luckily, I have no problem diving into my amps.
I've seen them go for as much as $750, and as low as $385. Around $600 might be a good price to accept, although, I would start higher.
They are great amps, I don't think you will have a problem getting rid of it.