I am getting some body work done on it and they wanna add dual exhaust because the body kit i'm getting is dual ported, so l wanna make sure l do not get screwed over.

The cost depends on what brand of muffler they use, l am assuming they will keep the original exhaust and simply be welding a new slot for a 2nd unit. For that type of setup it should cost you under $500. However, there is no advantage to adding a second exhaust without getting larger down pipes and a free flowing cat plus a air intake for the engine.

wow.they should pay you to do that.

it all depends on the setup. if you want a borla catback exhaust system it will cost you alteast $500 for the parts, plus an additional 100-200 for installition. if you really want more power, some headers and larger diameter pipes will also be needed. l would say to really get everything nice and to add power, you will want around $1000.