There is no technical reason they should be so expensive, components wise I mean. But the development and QA processes, and regulatory filings, audits, and all the other crap to make it suitable for medical purposes, make it so. That is why a WII balance board costs peanuts, but a medical device with similar functionality costs 10K. If has to be developed according to FDA regulatiosn, there need to be mandatory QA controls in place, software needs to be developed according to medical use standards, there is a regular FDA audit to deal with, liability, studies and validations, etc.
The WII balance board just needs to work. For a while. Non calibrated, non validated, and if it doesn't do what is expected in some cases, you get to call tech support instead of file a million dollar lawsuit.