mrbmwx5 has put 4.8is mufflers(left and right), each of the muffler is list priced at $819.40(see link below). If you are buying these from dealer, it will cost you over $1600 +labor. You still will not have as good sound as you will with Eisenmann or Remus mufflers for less price. Unless you can get some used mufflers, its not worth it.

RealOEM.com * BMW E53 X5 4.8is Exhaust system, rear