The average performance muffler for a sport motorcycle is around 500 bucks. the whole system ranges around 700 to 1200...
considering there are 2 large mufflers on the Borla system, at say 150 each... and 2 tips at around 50 each... and some fancy welds and sections of pipe... I think the system is fairly priced. It fits and works very well... And its so easy to install the average person with a 12 mm wrench can do it.
Wait till you have to change a tire... now that's expensive.