I didn't expect to have an update so quickly, but Adafruit just got their FONA cellular module back in stock, so I ordered one.

Far fewer pins than the Sparkfun module, and comes with Adafruit's open source library.  I'm excited about that, because it should save a lot of work.  The Sparkfun board only had an AT command reference to support it.  That said, Adafruit says the library does not yet support GPRS.  But the module does, so hopefully it will just be some quick mods.  Yay open source!

With that module replacing the one from Sparkfun, it seems like this entire thing is being built with parts sourced from Adafruit. The Beaglebone Black was from them, the GPS module is from them, now this cellular module.  If I don't use the bi-color LED for the door indicator, and use a NeoPixel instead, it will be one of the ones I have from Adafruit.  Camera module, Adafruit. The only remaining parts are the signal relays and the microcontroller with RF module.  One could use a standard Arduino, but for size and RF integration I like to use my own board, based on Moteino from LowPowerLab.  I use RFM69HW. They have signal relays too!  

Since the car itself is the "casing", seems like I will have to do zero manufacturing, expect maybe some support brackets.  That means no one will have to, and these should be just able to be assembled according to a recipe.