So how about low-power units in something like a NEMA23 form factor with some liPo batteries and a solar cell, with some rare earth magnets on the back? Put a cellular modem with GPS in it, and sell it through a website, where you can assign units to "flocks" or "clouds" and look at their data on a Google Earth style interface. So long as the bandwidth use is kept low enough, this can be done economically and within a power budget that would let these things run indefinitely.

Just having thermometers and microphones would enable a ton of uses. Like, how about in the energy industry, where FFT analysis of machinery sounds could be used for basic health monitors? You could sell a ton of those to the Energy Industry and they wouldn't bat an eye at $100 a unit. Just the ability to tell people to distribute them, then handle everything else from a website would be worth way more than $100 a unit for them. (The employment qualification bar for the more remote energy industry jobs is very low.)