Sounds like a lot of fun to make a clicker of your own! I guess I mistook what you mean by "it makes me consider getting a dozen orders for $50 and making more".
To justify for a price-tag at double of the parts' worth, I would wish those buttons to do some magical stuff. Assuming there are four buttons, well:
* Button 1: swipe from the middle of the tablet to the left, thus simulating a finger-swipe event to turn pages, and
* Button 2: swipe from the middle of the tablet to the right ...
* Button 3: specific to Boox device - toggle the orientation of the display between Portrait and Landscape, and
* Button 4: lastly, specific to Boox device again - well, may the button toggle their "Finger Touch" feature.
That's the wishlist, and my willingness-to-pay for such a clicker is $100 for the first one, and $50 for a backup unit
I think the Logitech Spotlight was priced at $100 upon release.