The key to the prices was finding the card in stock at a reputable vendor.  That is why I used TigerDirect and Newegg for my price/availability checks.  Doing some extra searching, I did find a 1GB 5870 from a vendor with some positive ratings that claims to have the card in stock for $419.99.  Everyone else lists it as a special order or out of stock item.  Considering it's a discontinued item, good luck getting any "Special orders."

Of course, you could always take your chances and buy a used one for only $249 from bobbyh!