Newegg offers the Runtastic Speed and Cadence Bluetooth Bike Sensor, model no. RUNSCS1, for $49.99 with free shipping. (B&H Photo-Video charges the same.) That's tied with our mention from last week and the lowest total price we've seen. (It's a current low by $10.) It works with your iPhone to track speed, cadence, GPS position, distance, and altitude.