Cateye Strada cadence goes for about 40 - 45$. It's wired though. I dunno how stuck to wireless you are. You can get the specialized speedzone like another guy said but you have to get the elite one, not the sport. The elite is like 50. Then you have to buy a seperate cadence kit for it. If you like Cateye and dont mind wires get the Strada Cadence. If you wanna spend 100+ cateye makes the Double Wireless which has cadence and is wireless.