A while back I was stuck in the hurricane evacuation surrounding Houston. I got caught in a 6 hour stop and go traffic jam; luckily it was in the middle of the night so the van did not over heat. But fuel was short and when I had a chance to fill up I all that was available was supreme. The next day the CEL came on.

I took it to AutoZone to read the CEL code and it was P0421 right bank catalytic converter.
I then took it to Firestone and they said it was the cat and the oxygen sensors - (3K to fix everything)
Further they stated Mazda should cover it.

It’s a 2001 MPV with 73000 miles on it. I think the emissions are Californian

So now a hundred bucks lighter, I’ m driving home from Firestone (about 3 miles) and notice no CEL. I guess they reset it. How long will that last?

What are my repair options?
Is 3K about right?

The CEL may return at any time or maybe won't at all if it was an intermittent glitch in the system. 3K sounds very high for an estimate anyway. The right bank converter on a California emissions system is around $850. Very unlikely that you should also need the oxygen sensors as well as the converter. I think many shops use this shotgun approach so that there will not be any chance of a misdiagnosis. California emission warranty will cover for up to 84 months or 70k miles on the converters only, not the O2 sensors. Since you are only slightly over in mileage and well under in time, there is a fairly good chance that Mazda provide a goodwill repair due to the expense of the part. Your local dealer can help with that although the light needs to be back on and P0421 stored. I doubt that they will take your word for it.