You may have trouble finding sellers at those prices here. Best bet may be to go Craigslist or try to low-ball some auctions on Ebay. I picked up a Sapphire 5850 Extreme on Craigslist recently for $120, but the fair market value seems to be more like $150 for used 5850s and closer to $200 for used 5870s right now. You can get them for less, but it takes some hunting (and hence some time). Used 5850s have held their value pretty well so far, since you could still get them new for around $160 less than a year ago.
I am trying to find that kind of deal here, I am in midst of a transaction atm. Will let you know.
Thanks for the advice.
I have also had my luck on eBay, 3 5830s for $240, 1 5850 for $120