Try this site http://www.midweekclub.ca/powerFAQ.htm#Q1

I would see if I can a used PowerTap or PowerTap Pro wheel. If not, you can get a new one for a little less here http://www.analyticcycling.com/Cycle...pProducts.html

Although the Polar is somewhat cheaper, the cost does not include the cadence kit. You also need a Polar s720 HRM model and the Power unit. Total comes out to $630+. Then, you probably need to spend couple of hours setting the unit up and it is not gurantted to work right off also. That was I like the Powertap but my wheel choice is restricted. I don't think I will win or lose a race because the wheels I am using.

Don't the HAC because it does not really measure watts. The power feature only kind of works when you are climbing. On the flats, I don't even know if it could report watts at all.