No, you won't need a "$30,000 computer". My $600 computer can play Crysis with all settings on high (plus the CFG file hack).
Crysis Warhead is supposed to be easier to run on computers (faster) than the original Crysis, they've made optimizations to the game engine.
they said in GamePlay Magazine that Crysis:Warhead could play normal on 400-500€ PC so that's around 800$ PC.