Looking for electronics help!

I want to build a spindle tachometer with a digital LED display. I just bought a mini lathe and a mini mill. I would like to have the display and controller mounted on my wall, and sensor wires running to each machine that optically detect the speed of the spindle. I can buy a kit for around 70 bucks, but thought that some electronics wizard might be able to help out. I will reward in like kind in a agreed upon amount of custom machine work.