I got a laptop for $400. It can run Blockland and most Valve games without a problem. Only Portal 2 does it ever have problems with, and that's simply because of the cpu-intensive moments like GLaDOS's reawakening.
It runs Starcraft 2, but not as well as people expect everyone playing Starcraft 2 online to run. It runs Oblivion just fine, but Bioshock it has an echo problem, as well as having trouble in combat situations. Still, $400 for a 2.1 GHz laptop wasn't bad when I got it.