Toyota Repair: P0420 Code - Catalyst System, p0420 bank 1, p0420 code

Question
Ted,
  Similar to your reply on 2/19, I also have a check engine light on my 2000 Avalon, 147,000 miles….diagnostic scope reveals code P0420 (Bank 1) as the issue.  I have visited 2 Toyota dealerships and one mechanic to directly review the codes and have called 2 other dealerships to review the best probable cause for the reading.  All offer completely different courses of action to resolve.  

I don't need you to be exact; I am looking for the most probable cause since one of the options include a $1,000+ repair and 2 repairs options under $200.  The first option was to replace the spark plugs and “that should clear up the code” $150; the second option was to fully replace the catalytic converter $1,050 – this converter is only available through the dealership, the OEM replacement market does not have volume and considers the car too new for replacement of this piece, therefore there are no other sources; the third is to replace the O2 sensor BEFORE the catalytic converter, $175.

I am not getting a straight answer, even from Brand dealerships.  If one of the sensors were at fault, would a separate code appear?   I need the plugs, so that option I am prepared to take regardless, but the other 2 options are up in the air  - one option is 1/10th the cost of the other.  Any recommendations?

Thanks,  

Answer
You can have the spark plugs replaced but it will not solve the problem, neither will replacing O2 sensors, O2 sensors will give different codes if they fail, not a PO420 code, this code specifically states "catalyst system performance below threshold" to put it in simple terms the converter is not working anymore and needs to be replaced.
If you live in or near a larger city I would recommend looking for a muffler shop that has an aftermarket converter they can install, if not, the other choices are pay the $1,000+ or trade it in.