One of the following needs to happen:

1) You diagnose and fix the P0420
2) You take it to someone who will diagnose it and fix the P0420
3) You take it to a muffler shop and have the converter replaced to see if that fixes the P0420.

Here's how to diagnose the P0420 using Torque Pro:

 

Mechanic took a look at it today, the catalytic convertor is shot

He won’t have a quote until Tuesday, any guesses how much that is likely to run?

 

To answer my own question, I just get the quote $470. Not as bad as I was thinking, but still nasty. Add that to another quote, nearly as high, to install new plugs, wires, and coil (just a bit beyond my skill/patience level given the location of the plugs, and the rivets on the coil), and I’m looking at a lean couple of months.

 

Take it to a small independent muffler shop (not Midas, etc) and have them weld in a universal cat converter. That should save a lot. As far as the price for plugs wires and a coil, I really doubt the need for a coil. And again you should be able to save a lot by going to a different shop. This one is taking you for a ride IMHO. Have you priced different shops for the converter and for the plugs/wires? $900-$1000 for a converter, plugs, and wires - I think not.

Whatever you do just make sure the acceleration is normal again before putting on the catalytic converter. Misfires can ruin converters in fairly short order, and this is probably what happened to your original. Engine misfire took out catalytic converter. Still, it should have set a misfire code - so that is strange to not set misfire codes if you have enough of a misfire you can tell your power is down. That is the wildcard here.