Read the following link for the exact code description:
http://www.iequus.com/obd_def.asp
Your car has 2 O2 sensors. There is a front one identified as bank 1-sensor 1 (it's in front of the converter) and a rear one identified as bank 1-sensor 2 (it's in back of the converter). Is your mechanic going to replace both of them? The OEM Toyota sensors run about $135 each at the dealer. The front one should take about 10 minutes to replace; the rear one about 30-45 minutes. I would say an independent mechanic should charge about 1 hour of labor to replace both sensors.
You can buy aftermarker sensors yourself at just about any auto parts stores and install them. Some of the aftermarket ones require you to cut the 4 wires off the OEM connector and splice the 4 wires of the new sensor back on to it. You will need a special O2 sensor socket (about $10-$15) or an open end 22MM wrench. The front one is located under the hood and is easy to spot. It should be obvious how to remove and reinstall that one. The rear one is under the car in the exhaust pipe after the converter, and it's electrical connector is under the driver's seat, and is accessible by pulling the carpet to the side where the floor vent is for the rear seat passengers. For the rear one you disconnect the electrical connector inside the car and push it through the floor of the car toward the outside. Then you can unscrew the sensor itself from the exhaust. I recommend tying a long piece of heavy string to the connector before pushing it through the bottom. Then, once out, you can tie the new connector to the string and pull it back in to the passenger compartment of the car.
Mike
It worked fine until I fixed it! 
Linear Mode
