Went to my local radio shack to buy some supplies to really get started on my robot project this weekend, and to my amazement they still had a large display of Zip-zap Rc cars and accessories. It was mostly just zipZap SE cars and replacement body kids, but they did have the Zipzap monster truck upgrade kits. Each kit contains 3 different motors (8k, 14.5k, and 21k rpm) and a set of two gears for each of them. And they're marked down to a clearance price of $5.
On inspection back home, the gears were an even better score than I thought; for each motor, one is a large hubbed gear with a square bore, presumably made to attach to the axle on the zipzap monster trucks. The others are dual gears about 1cm in diameter, and the major gear on all three has the same diameter and number of teeth, so the three can be used as a set of matched single gears.
Huzzah! Unfortunately, they were out of photoresistors, but after finding a cache of cheap motors and gears, I hardly cared. Beats paying $5 plus shipping for a single pager motor!