$150.00 or so (though I could be off) to raise the limits on the CEL logic.
0420 makes much more sense..
So, you changed
the plugs (double plats, gapped at 0.054"?)
the wires
the fuel filter
the air filter (or cleaned the filter)
cleaned out the UIM/LIM/TB of crud
gave the car a good spirited run to get the cats going, and
tried running some berrymans through about 4 or 5 tanks of gas to help revitalize the cats?
I hope you attempted all of that stuff before resorting to a new cat.
Ray