You can choose between TWO options:
a) Dual exhaust from your Y-Pipe (stock midpipe):
* There are dual exhaust for the Y-Pipe out there in the market, just find the one that best suits you. MagnaFlow, FlowMaster, etc... Youtube them, they'll have a lot of clips on what to expect in sound. All that a muffler shop has to do is bolt on the dual catback exhaust from your Y-Pipe. Add some hangers, and wah-lah! Dual exhaust for your pony.
b) True dual exhaust (Modified Y-Pipe or H/X Pipe):
* When it comes to true dual exhaust, both your exhaust manifolds (headers) will have their own piping straight all the way to the rear of your car. A
modified Y-Pipe consist of cutting, and welding. It's like splitting the Y into two separate piping. Still with me?
Man, there is so much to type...when you could easily find your answer here:
http://www.allfordmustangs.com/forum...r-threads.html
Look through these threads, and you'll figure out what you'll want. It's seems to me, that you're looking to spend at least more than $450+ based on parts and installation.
I'm only 19 man, and gosh...I've reached $1188 on my mods.