I created a Mouser.com project page to facilitate ordering of the parts for this project: http://goo.gl/kvc0AO. Caveat emptor, I have tried to make sure the parts listed there are correct, but have not yet placed the order myself.

Note that, as mentioned in the details section above, the Mouser project page does not include the items that cannot (or should not, for price reasons) come from Mouser.com.  I.e., the PCB, the battery, and the motors come from elsewhere.  (See updated BOM in the Github repository for details.)

Note also that I am not partial to Mouser...it just so happens neither Newark nor Digikey have the requisite battery holder in stock, and to control shipping costs in makes sense to get everything from one supplier to the extent possible.  (I still use aliexpress.com for the motors since they have them very cheap there and free shipping, and Ebay since that is the cheapest source for the batteries, and the seller ships for free also.)

I would like to find an inexpensive rechargeable coin cell with solder tabs with reasonable discharge capacity. The solder tabs would enable a smaller footprint.