You can get 15% off your first order here: http://bicycleoutfittersindy.com/index.htm that is how I got my 500. Look into a Bontrager cadence sensor (if you only want cadence) they are around $30. Bontrager also has a speed and cadence sensor not sure of the price. I let the GPS determine the speed for me.

Edge 500 is nice!

Norm