Measuring motor speed

[fovea1959]

I'm struggling with a good way to measure motor speed for our shooter motors (probably Banebots, probably 10-20k rpm). I'll have a back shaft available for mounting.

Any one have any advice for something off the shelf? my priorities are available, reliable, simple to interface, easy to mount, and cheap, in that order. I'm trying to stay away from have to do any electronics design (I'd end up doing it myself, I suspect, which is not the point of this exercise!), want to use off the shelf if possible. Alternatively, something that we can put together on perfboard would be good.

If we're on our own, we're thinking either Hall Effect, or else opto (fairchild QRD1113/1114 with a black/white "plug" on the backshaft), but if someone has something simple that they know works, I'm all ears....