Everytime I start my 2002 Monte Carlo SS the service traction system light comes on, but it turns off after a little riding. The Trac light by the speedometer is always on, but when I hit the button to turn it off it doesnt do anything. The garage says not to worry. Should I be concerned?

 

It is more than likely your wheel speed sensors, or wheel bearings. The Speed sensors attach in to the back of the wheel bearings. They sometimes get dirty or corroded, and the wires themselves become very brittle and crack/break. Your brakes will work and your car will drive but you won't have abs. There are quite a few posts on the forum here with step by step instructions on how to change the wheel bearings (if that is the problem) if you can get someone to read the codes for you to verify which it actually is, it would make it easier for you to trouble shoot.

 

If the wheel bearings are the problem. Can you give me a realistic estimate as to how much it should cost to have a garage fix?

 

not having done them to my car I can only give you an estimate.
You can buy the parts on ebay

Front 2 NEW Callahan Left AND Right Wheel HUB Bearing Assembly Pair With ABS | eBay

for approx $200 by the time the dust settles, there may be cheaper options that is just the first I got when I did the search. My guess on labour would be about 1 hour per wheel, so $120 - 180 depending on what your garage charges. So you can ball park around $500 to have a garage cahnge both front or rear. If you have a friend that can do it, I am certain it will be even cheaper. Or if you are mechanically inclined yourself here is a link to a video showing exactly how to do it