Air Bag Light On problems of the 2002 Oldsmobile Bravada

While sitting at a traffic light I noticed the service air bag light was on. I had seen this before while I was driving but it was only a flickering light and not a steady light. After driving home I noticed the light was again off. This happened again a few days later, and the light continued to be on for about a week (when the engine was running) and then it went off again. This time it was off for only one day. Now the light is on all the time when the SUV is running. I took the SUV into our mechanic and he tried to pull up an error code. He said that it could be a corroded wire or it could be the entire air bag(s) need to be replaced. He also stated that if one air bag is not working that none of the others will either. The price quoted to fix this is from $150 just to see what is wrong, and up to $1200 to replace airbag.