I have a magna flow and I went to a shop and had them weld on a cat back 2 1/4" with a matching resonator. Sounds great! Paid 120 for it.
You can have just the muffler installed, i had my first muffler, arospeed, installed before and the exhaust shop made a custom pipe that runs from the connection (above the rear axel to the muffler.. that was $60.
but I recommend the cat back, does help sound and performance.
Arospeed (Muffler only)
Magnaflow Cat Back