how much does it cost to get a nice dual exhaust set up?

You will probably get a lot of different answers, depeding on the system, shop installing it. I have a Flowmaster system, dual in dual out. non stainless (stainless is way more durable but much more expensive). 3 diameter, 24 inch long rolled edge tips. I paid $375 out the door.

Do a search, there are countless threads on this.