Fabrication or other?
 

I was wondering what the size of the piping is on a stock ek ex exhaust? And whether getting a professional to fabricate an exhaust would be comparable to a bought system. The guy I have in mind is VERY good (worked for flowmaster for years), so should I just tell him a certain size and let him go to town? He did my friends' exhaust (header back) for about $70, and welded a muffler on. Thanks in advance!

Cost depends on what tools you have, and who's "bought system" you are referring to.

Get a quote from your dude and compare to kits you find on line. Car parts stores usually sell pipe size adapters / changers for exhausts (say, 1 1/2" to 1 5/8", etc.) if you go the DIY route, but they aren't going to have anything extreme (like, say, 1 1/2" to 3 1/2")