EDIT - Oh, knackers. Looks like this isn’t actually true, just someone’s fantasy (see comments). Cheapest option for Mocap remains Ipisoft. Dammit.
Ooh! Looks like a major player’s getting into the cheap mocap game - Adobe have just announced a suite named “Gollum” which will perform mocap using the Project Natal cameras.
Cost? $400. Time? No idea.