Grady wrote:
Strictly spindle speed. ... not cost an arm
and a leg, and that I can assemble myself.

At the bottom for cost would be a bicycle speedometer. I use a Sigma
Sport on my drill press. By using the kph mode and setting the
circumference to 1666mm (IIRC), the speedometer reads in 10's of RPM.
E.g., 30 kph at 300 rpm. It uses a magnet and pickup. Works to about
3300 rpm, IIRC.

http://www.cccyclery.com/sigmasp.html

Bob