Hi,
Actually these optical capture device to turn a screen into the interactive whiteboard has been in the market for quite a while. However, it did not take off very well maybe due to the issue of blocking and also the lack of commercial push for these.
I have seen another one from a Japanese brand selling for about SGD 1000, where they claim to be using high resolution optical cameras and connects via USB. Therefore, the advantage of these devices compared to using the Wii Remote may be high tracking resolution, wide viewing angle and potentially plug-n-play.
Unless they manage to scale the manufacturing and sell plenty of units, it is quite possible that it is quite costly like you have seen.
Regards,
Boon Jin