Deven, yep I already had that site and I also recommend it as they even came out ahead of rockauto by a few dollars along with others including ebay for the rear oem o2 sensor at $101 total, but for the front oem o2 sensor ebay was the best at $74 total. The next best price was at rockauto for $86 total and at oxygensensors it was $89 total.
Toyota emission systems are sensitive and tempermental with anything but oem. That has been a issue for years so I wouldnt buy a aftermarket cat converter either as people have had problems with those also.
How many miles on yours when you replaced the o2's Deven? Mine has 89k right now with no cel on Im just replacing them because this is the range where people start having problems with them on toyotas, and to see if my mileage will improve. If not then the next step is getting a new cat converter since I wouldnt be surprised if the original is clogged as its not rare to hear of it with toyotas. Ive done everything else I can think of to improve mileage to no avail. New plugs, new pcv, cleaned maf, recharged air filter, seafoamed tank and crankcase, keeping the tires filled, alignment ect.