[Staples] Clearance Bluetooth Bike Speed and Cadence Sensor after 25% OFF YMMV: $15
It's a rebranded Wahoo sensor. Great if you're using Runstastic, or Strava to ride, and excellent for on the stationary trainer.
My local Staples (14th and Markham Rd) had half a dozen in stock.
Link to image:
Amazon is on glue selling it for $127CDN in comparison.
https://www.amazon.ca/Runtastic-Cadence ... +runtastic