Those are the old thimble-style O2 sensors if I'm not mistaken. They do get really lazy as they get older and are pretty cheap, so I'd suggest changing it out.
You may have a lot of carbon built up in the combustion chambers from the cheap gas. Try a higher concentration of additives; some have also run a few ounces of pure acetone (IIRC 3 oz per 10/gal fuel) into a full tank of gas, there is lots of info on the web about it. It's much less expensive than branded additives.
One additional idea: the butterfly valve at the throttle body can get pretty dirty with a lip of carbon and other deposits, so open that up, spray some carb cleaner on a rag and wipe it off. It's a common problem on all makes and models and contributes to rough idle.
Now I'll school you about what car you really have and how to budget.

Seriously, good luck with all of it.