It is not likely that you need a new catalytic convertor. The error code you are getting for a cat convertor is triggered by the rear oxygen (HO2) sensor. Its function is to tell the computer that your cat convertor is bad. However, the computer can't tell the difference between a bad sensor and a bad cat convertor.
It is almost always only a bad sensor.
Try replacing the rear HO2 sensor first. Get the DENSO sensors. If you get the OE sensors, they are original equipment and fit perfectly. Go to the DENSO web site,
here, and find the DENSO part number (see below). You can get the DENSO parts in many places on line. I commonly get them from Amazon.com for cheap. Search Amazon.com for "DENSO 234-4048" for example, and the first choice should be the correct part.
Here are the part numbers for your vehicle from the DENSO website. (Note that if you are also going to replace the front sensor, and if you have a 4-cylinder engine, you will have to call a Toyota dealer parts department and give them your VIN number and find out if you have a Calif. emission engine or not).
DENSO part numbers:
Front sensor 4 cyl Calif. 234-4622
Front sensor 4 cyl non-Calif. 234-9010
Rear sensor 4 cyl all 234-4048
For the above rear sensor: See
here
Front sensor 6 cyl all 234-9047
Rear sensor 6 cyl Left all 234-4261
Rear sensor 6 cyl Right all 234-4064
For the above sensors, see
here and
here
Here is the DENSO web site URL:
http://densoproducts.com/resultsApp.asp