I'd be happy to join such a group. Using the Arduino, I've built a few gadgets to help my Parkinson's. The best of which are:
- a data logger to measure my movements 24/7;
- a box that beeps when my posture gets bad.
Each is the size of a small pack of cards. The components in each cost about £20. But, if built in bulk, I suspect you could build it for under £5.
I find that the step from having something working on a breadboard (a device used in electronics to build prototypes without soldering) to having it wearable is very difficult.