What kind of business would benefit from a really cheap eye tracking technology?

Security and surveillance industry.

Here are some ideas I came up with after being exposed to a variety of industries. In summary, most of the ideas revolve around Driving Assistance - Tracking where the driver is looking and comparing to activity data collected from radar/IR/cameras to alert the driver of activity that may not be in their current focus. This could benefit truck drivers significantly. Advertising - If you could have a very sensitive camera track eyeballs from passing cars on billboards, you could more accurately collect data on interest level and engagement with the ad, identify demographics, perhaps even track if the same car has passed twice and looked at it multiple times. Entertainment - We already pass out 3D glasses. If you gave the wearer some sort of augmented movie experience but tracked their eyes, you could poll data from entire audiences about what in the frame they are paying attention to. Sports training - Many times in sports, training what the player is paying attention to or delivering insight on how plays can unfold can be enhance the speed in which a player develops. For example, quarterbacks have been notoriously exploited for their tendencies to look for particular receivers or going through particular progressions. If you could both track their eyes to determine where they're looking and point out tells they may be projecting to the opposing defense, you could eliminate vulnerabilities in their playstyle. Construction - Having eye tracking to guide measurements to be uploaded for site surveys or to confirm dimensions.