By way of an Amazon review by RobinTaylor9640:
Loved the book, especially the Jitterbug Project, but the author did miss an alternate source for the vibrating motor in the bug though, battery operated electric toothbrushes have one and are cheaper than Radio Shack if you shop around, assuming you don’t have one already lying around the house, of course.
Excellent tip! These are 3volt motors (just like the cellphone vibrator), but beefier–which can mean more rattle for your buck (depending on how toothpaste-caked the motor is). Definitely worth saving that broken toothbrush for parts.