I bought all of my 3" round from here. If I remember correctly, there pricing was pretty good.
http://www.mandrel-bends.com/catalog/
It was nice stuff. It's just all cleaned up and bagged like something from Vibrant etc.. I just scrubbed the oil off of it with soapy water before using any of it.
I used oval tubing from Vibrant to make my exhaust from the headers back to the mufflers for additional ground clearance and just because I don't like to see any of the exhaust below the rocker pinch weld..... I will say the oval stuff is spendy though.......
You can click around through this blog to see which kit this guy used. I find myself referring to his pictures fairly often during my build. I think he may have used a Stainless Works kit, but I can't remember - - Regardless - it's a really good blog.
http://67novaproject.blogspot.com/
Good Luck!