I just picked up a GTX 460 in that price range at Fry's. Looks like they still have several available (at even lower prices). I'm not sure if they ship though.
Newegg has a few in that range - The 1MB cards perform better than the 768MB cards. GTX 460 Cards
Make sure you've got a big enough PSU and an available PCI-x16 slot before you purchase anything though.
I have a pci-E 2.0 slot. ANd how do I find the PSU info of my computer
Here are my specs:
Version 6.0.6002 Service Pack 2 Build 6002
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name JOHNBOY-PC
System Manufacturer Compaq-Presario
System Model KY700AA-ABA SR5807c
System Type x64-based PC
Processor AMD Athlon(tm) Dual Core Processor 4850e, 2500 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Phoenix Technologies, LTD V5.36, 11/19/2008
SMBIOS Version 2.4