Toyota Repair: Toyato front air sensor, emission control device, smog test

Question
Hello, Our check engine light came on this morning and we took it up to the local repair shop. They called and said the front air sensor needs replacing.  My question is how long can you drive with a front air sensor out? Will it harm the car? It's 1997 Corolla with over 80,000 has been running great until today. The shop mentioned that they usually recommend replacing both air sensors at 60,000 miles but folks don't do that cause their costly.  The quote was $175 for the part. Is that a good price for Seattle? Thank you so much for your help.  

Answer
I think what you are talking about is the oxygen sensor in the exhaust manifold, this is an emission control device and normally doesn't affect performance and the car will operate normally,you can drive it in this condition for as long as you like but it will have to be taken care of before the next smog test or it won't pass, the price to replace it sounds very reasonable.