I realize this is an old thread but what shop did you go to here in Colo?Apples to oranges comparison, but I went to a muffler shop that does a lot of 100 series in Denver CO. I brought them a set of DT headers, OEM gaskets, and a full set of studs. They charged me $600 USD for the install.
Having said that, shops were all over the place. When I got quotes ranged all the way up to $1600 just for the install.