I agree. first off, what makes you think your cat is going? do you have exessive oil consumption? are you running rich? if your cats are clogged you got other things to worry about such as fouled spark plugs, fouled o2 sensors, etc.
have you smelled your exhaust? if it has a strong sulfur/rotten egg smell especially when you rev the motor up a little, your cats are getting clogged. if you don't have a check engine light for your cats, it's your secondary smaller cat (less serious) if you do have a CEL for cats, then looks like you will have to change your main cat. I agree with pcb that you're simply best off waiting until the car physically fails inspection before spending ridiculous money on a new cat. if that is your only option, I suggest you find another protege at a scrapyard and cut out it's cat. save yourself a good amount of money. hell, you may as well drop in a new or better engine for the price it will cost you to get a new cat.
now... if you are lucky, you might be able to unclog your cat at least partially by doing some full throttle pulls, provided your engine and transmission is in reasonable condition. the key here is to bring the engine up to redline at least 2-3 times in a row so the engine gets nice and hot and hopefully clears up the cats a little. you will also give your injectors a good clean. if you open your window after the full throttle pull and it smells strongly like exhaust/cat/rotten eggs, then you did clear something out. I don't recommend doing this if your car is running rich however, as you will just make things worse.
what is your mileage, how do you drive the car, and what sort of oil consumption are you experiencing?