Yep 4.6/4.8is rear valance, new from BMW you're looking at $550 bucks since it's 3 pieces.

Try to find one used off a parted out X5, you just missed one in the classifieds.

The 4.6iS front valance I also found went extremely up in price, just 2 years ago it was right around $300, now its $440.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards