dirt cheap DC motor with battery holder

Your local megastore might be selling electric toothbrushes, two for
seven dollars (USA). Includes a sturdy plastic case which houses the
motor and two AA batteries with an easily removable cover. You can
remove the whole assembly by bending the latches inside of the
battery case and pushing in from the other side of the case.

Not necessarily novel, but I like the design of the switch, one flat
piece of metal.