OP, you have similar concerns to me. Wanted a better sounding exhaust without breaking the bank, maintain all emission standards and not take a chance on voiding any warranties. Please keep in mind, I do not plan on doing any additional mods to my car, this is it, as far as the engine is concerned. Good info from jcosta on this link below.
Trying to understand the cumulative effect of breathing mods
Was initially planning on going w/Fast Intentions, cost w/shipping to HI is over $1,600, plus the local performance shop I would use for installation charge is $150. The owner of this shop would put on any exhasut I ordered for $150 but gave me two other options. Either one of these would cost only $400. Replace stock muffler w/two seperate mufflers from the last flange (this would cause 2 bends by the mufflers) or cut the existing pipes before the last flange and weld larger 2.5" pipes which attach to mufflers for a very straight exhaust flow. I chose option two, pic attached.
Very happy with my choice as this did not add any weight to my car, sound is much better than stock, original exhaust tips were kept, my butt dyno feels like their has been some increase in power, plus a savings of over $1,350. Might be an option for you.