i am looking at Borla as well, I dont think they make an axel back kit, unless you go with there universal exhausts. They make the cat back which is 899.99, which I think I am going to go for.
Borla does make an axleback. Another option is ford racing FRPP GTs. They are made by borla but have a 3.5" tip instead of a 4" tip. The FRPP GTs will run about $50 cheaper than bolra stingers. At ninosports the borla stinger are $549 and the FRPP are $529. Here is the link: 2005-07 Mustang GT Axle-backs
I got my Frpp stingers from 50resto if im not mistaken. They sound great with the stock H, but they sound really good with the off road Xpipe. It sounds good to me because its what i wanted, sounds like a raspy F1 race car. But if you are into the old muscle car scene type deal i would look into maybe some other type of mufflers. Or atleast matching these up with an Off Road Hpipe. That doesnt sound bad at all either. Just not as high pitched, but very deep and "grumbley".... If that makes sense?