You could get a header and relocate the cat under the car, but I don't suggest removing it altogether. But a header will cost around 500 US$, so its up to you.
You COULD remove the cat, and replace it with a straight pipe, but you WILL get a permanent check engine light. I'm not sure hope much power you would gain tho, and it certainly would not be worth the damage to the enviroment that you would be doing by running without the cat.
Unfortunately, both of these mods will void your warranty.
Just get the cat-back for now, and do some more research before you remoce the stock exhaust manifold and cat.
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