The Wii managed to package what was originally a $250 to $500 MEMs inertial sensor into a $35 video game controller. The Swiss Ranger 4000 time-of-flight camera from Mesa Imaging is currently down to $9095 and gets you 176 x 144 pixel resolution with depth from 0.3m to 5m +/-1cm. Canesta, on the other hand, supposedly has development kits and their sensor has been integrated into actual shipping consumer electronics where they have been integrated into a laser keyboard for $149.99.
I am a bit curious how Microsoft plans on bringing the cost down if the project Natal controller is indeed a time-of-flight camera. However, Microsoft has recently stated that the ZCam Time of flight camera from 3DV did not contribute to project Natal. So perhaps the controller is something more like this project but using parallax and infrared shadows to pull out the 3D geometry.
I don't care how it works, I just want one of these sensors now.