I am not sure what you definition of affordable is. But for $249 you can have the Wahoo Bolt that was just released on Wed, and does what you are looking for. The HR, candence and speed sensors communicate with your phone, and the phone displays on the computer.

I am too much of a newbie so I don't have permission to post links. So you will have to copy/paste

wahoofitness.com/devices/bike-computers?rmsrc=1&gclid=CjwKEAjwkq7GBRDun9iu2JjyhmsSJADHCD_HP83YyWmwIiSrfzRsoMXXEQgPXmJKwlwDa8dQN4gi iRoCSS_w_wcB