What would be best to add performance/sound? A CAI w/ smooth transitioning in the pipes, or a mushroom style intake or just what kind of intake? (All which I would try to get smooth transitions through the pipes)
It depends on what type of vehicle and engine your running to know what youve got got and what your trying to get it to do. Example in a diesel a CAI while allow more airflow and thus more power while it will also increase the volume of the turbo whistle. However you have to be weary of the brand as certain airfilters K&N and AFE are known to let small amounts of dust through and damage turbos. Most intakes have a sooth airflow path through the intake tubes. The "mushroom air filters are simply to give more surface area in which to filter the air and plug up slower. In an suv using the stock air box the filters may give less restriction to air flow and a minor mpg and power increase probably not too noticable while maintaining stock sound. But again the best choice is depndant on your vehicle and engine type to truly make any recommendations.
I think if you went to a good muffler shop it would cost about 150-200 depending how far you want to run the pipes . You have to look under there & see what you got & what you want to do. Do you need to keep the cats ?? Exhaust out the side or rear ??
For the whole system? I would just want to run the pipes coming out of the rear of the truck, not the side. If cats is catalytic converter then I would probably rather not keep it just because it will increase how loud it is and it will slightly improve my mpg and hp. (Only like 2hp more, I know)