Budget $315 max.
Buying from reputable sellers on ebay.
I used to have a Dell Latitude with a Geforce 64 mb gfx card w/ 1 gb of ram and a p4 1.8ghz processor.
It ran all of those games with the exception of world in conflict, nfs shift and halo 2
here is a video of a 9100 playing cod Modern warfare with the same specs I listed only 2 gigs of ram...