Doesn't spin fast enough? Baloney.

How fast are you spinning the engine when you flip-start it? Nowhere near the 1200RPM a typical cordless drill spins. Many people flip-start their engines exclusively.

The procedure for starting an airplane engine is not: Fill the tank, attach the glow plug driver, apply the starter, and crank crank crank crank crank crank crank crank crank until it starts. If you're doing that, or feel you have to do that, you're doing it wrong. Generally, a prime of 2-3 turns after you've drawn all the air bubbles out of the line going to the carburetor is all that's necessary to get an easy start.

I doubt you'd be saving anything by trying to convert a drill into an electric starter. You need to have a cup and cone machined, or you need to buy a replacement cup and cone for a regular starter. Tower Power starters, which are identical to the more epensive Hobbico starters, are only $17.99.