Based on a recent teardown conducted by UBM TechInsights, it looks like the most expensive part of Microsoft's Kinect is the box it comes in. According to UBM TechInsights, the Kinect contains about $56 worth of hardware. Around $17 of that cost is attributed to the PrimeSense motion detection system, including the microphones, cameras and processor.
Of course, the $56 figure doesn't include manufacturing costs (not to mention some undoubtedly massivemarketingcosts). It's also worth noting that UBM's assessment is just an estimate and only Microsoft knows the real cost. Still, assuming the figure is even close to accurate, it would seem Microsoft makes an impressive chunk of change from the $150 price.