It's rumored that it costs $150 for Microsoft to make a Kinect.
http://www.develop-online.net/news/35198/Source-pins-Kinect-...
http://www.develop-online.net/news/35198/Source-pins-Kinect-...
http://www.crunchgear.com/2010/11/04/what-kinect-looks-like-...
Note: I'm not making any statement about the possible awesomeness or lameness of the system. All I'm saying is the parts aren't expensive.