Couple minutes of Google at local library came up with what I think is mine:
Item # LCD8010Y07, LCD8010Y Self Powered Engine Tach/Hour Meter sparks every other engine revolution on ENM Company
Says single $25 but a few guys at the airport got together and bought them for about half that. IIRC the half dozen I ordered came to $85 shipped. Certainly a fraction what I paid for Tiny-Tach (not so tiny price).