Everyone has rightly pointed out that the cost of this sort of device is inflated by regulatory headaches and liability concerns. Let's not forget simple economies of scale here. A video game controller will likely sell millions if not tens of millions of units before it's eventually retired from the market. A medical balance board, on the other hand, is at best a niche device whose sales will likely be at least an order of magnitude (or two!) smaller. The costs of designing, testing and building this device are borne by a comparatively tiny number of sales, hence the higher price.