zenocchio

I have a check engine light every once in a while, related to the O2 sensors.
I had leaky injectors in the past, therefore I believe that my c-ats and oxygen sensors got damaged.
I have already the post sensors and replacement used c-ats and looking into getting the upstream. So far the cheapest ones I found are on rockauto, do you have any suggestion for cheaper ones? I know that someone is using the 335 ones for example, do you have any experience with this?
thanks