The Pre Cat is 80 each and Post Cat is 90 each, there are 2 pre and 2 post, so almost 400 bucks including tax! I checked below and there are a lot of clips holding them up as they route and the passenger side it looks hidden and hard to get to.

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2003 BMW E53 X5 4.4i - M62 engine (Non Sport with Premium and Cold Weather Package)
Color: Steel Gray Metallic
Mods:4.6is Exhaust (Pipes, Mufflers and chrome oval tips) BMW Sport package Taillamps, BMW Tire Valve Stem Caps
Medium tinted front windows
JVC HD Radio
Alpine 4x100 channel Amp
Orion 600W Mono HC Amp
Three 12" Sony Xplode in subwoofer enclosure