2 of the 4 O2 sensors on my '99 Lexus are not working. Where can I buy them without spending hundreds of dollars, which is what my mechanic says they cost. Online I see them for a wide range of prices, so not sure if they are good or not?
Rockauto is usually a good place to shop. For this car, Denso is the likely OE supplier to Lexus (Toyota).
You can cheap out on this repair and maybe all will be OK, or maybe you will be paying to change them again. The risk is on you if you buy the parts and hand them to your mechanic.