Jumping ahead from the "what" to the "how", I'm curious if you've thought about the ability to re-program (aka add features) to whatever you come up with. Specifically I think "We" have become accustomed to the idea that our software "apps" in our smartphones, tablets, PC's, etc. are constantly being updated/refreshed with the latest and greatest.
So the hardware becomes the bricks-and-mortar...and the software can be fluid. That said, there are many options but the two that stand out for a LOW-COST solution:
1. A $2-3 Arduino with a USB loader. AFAIK, this requires the end-user to download "unique" software. If functionality is changed you need more than drag-and-drop on your PC/laptop. I highly doubt the typical OGR end-user will be writing code. Hence feature upgrades would be done by the handful of guys here on OGR that know how to do it, and the executable would be made public.
2. A microcontroller (it could be an Arduino) that reads a $2 microSD card that contains the software. So if you upgrade the app, you simply post the new software on OGR and leave it to the end-user to drag-and-drop the new software into the microSD card and then plug that card into the signaling board. Most people have smartphones and "get" the concept of the microSD/SIM card and should be able to move a file from a PC or whatever to a microSD card without loading custom Arduino "loader" software.
This is a brave new world. Again, I realize I'm jumping ahead but I believe this can fall in line with not-to-exceed $10 (or whatever) cost target.
