This may depend on the manufacturer of the treadmill. I currently have a model that was purchased at Sears and (allegedly) their service techs are the ones to rely on. Being skeptical, I called the tech support number found in the manual and they also referred me back to Sears.
If you're not comfortable with the manufacturer rates, you can always try your luck elsewhere. I spoke to a sales person at Dick's Sporting Goods in the area and he was able to give me the number of a repair technician that works for the chain and also does side work. My guess is that you can likely find the same cooperation in other sporting goods stores.
Josh
January 2009