Oxygen sensors

I have a 2000 2.7 Tacoma that seems to go thru oxygen sensors every three years or so. It has the CA emissions package on it so I wasn't sure if that could be the reason why, since it has two catalytic converters on it. My questions are....does anyone else have the same issue, is there a place online to get them (sensors) at a decent price and shoud I replace the cats to see if that will help out?

 

I'm still on the original o2 on mine. Front or rear o2? They shouldn't die that quick. Run a denso or ngk. The dual cats shouldn't be an issue with heat. Do they looked clogged? Sounds like the motor is giving you a bit of a warning something isn't running perfect.