x3 on taking it to a muffler shop. I've got a flowmaster muffler, and have got many compliments on it. You will def hear a difference, but its not obnoxious. I like it and wouldnt dont regret getting it.
So just called the local shop, was quoted over the phone with $290 to swap out muffler w/ labor included (this included a Y-pipe needed). Lifetime warranty on muffler as well. I'm going to take it to another local shop who doesn't specialized in mufflers but said he might be able to weld the rear seam to buy some time.
You don't need the Y pipe - you just need a muffler with 2 in 1 out and a shop can run the piping without the Y. In fact, many of us delete the Y pipe because it tends to restrict airflow. I bought my muffler online and brought it to a shop. They ran bigger pipes, and deleted the Y for 100$