I wonder how well the hardware would work with an input system like Dasher. Dasher was experiment in statistical inference and tries to be an accessibility tool as well. http://www.inference.phy.cam.ac.uk/dasher/. I found it really fun to play around with and could get decent speeds but not great. It's true about eye tracking being prohibitively high. When we order an eye tracker for the lab, it ended up costing us £10K.