400-600 was the price i was thinking
If your husband is using an 8800GTS, chances are that the rest of his computer isn't really fast enough to take advantage of a $400-600 graphics card setup. It would be very helpful if you knew what CPU/Processor his system has.
Otherwise, don't bother spending more than $170-200 on a GTX560/560Ti/HD6950. Also, to begin with it's ill advised to spend $400-600 on what essentially is a 2-year-old generation of graphics cards. We are really close to a very large performance increase in graphics after almost 2 years of limited gains. If you want to spend $400-600 on graphics, you should wait for HD7900 series, which is rumored to arrive in January 2012 (and probably make sure your husband gets a new CPU then!).
EDIT:
OK-just look through his system and I think this may help. This is all Greek to me. Here is some of the things listed:
something is a XFX781
XFXnForce 780i 3way SLI
That's a very old setup. Such a system can be using a 2-core processor or at best a slow 4-core CPU.
If you have a chance to access his computer, just click Start, and in the Search menu type:
Dxdiag.exe, press Enter
Under System, read out the Processor.
My guess is, something like an HD6870 or GTX560 is the best bet if he has a dual core CPU.