This seller is accepting 80-cent offers for these cute little gearmotors: http://www.ebay.com/itm/112314392085
Same diameter as an LR44 watch battery, they are designed to accept a single 357 battery, friction fits nicely in place. 9 mA no load at 1.5V means that in a pinch, you could carefully
drive this directly from micro output pins with a few dropping diodes.
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."
- Pablo Picasso