Check Autotrader.com or cars.com. That will give you an idea. Prices might vary some for very similar 4.6s. I looked recently to see what they are selling because I am thinking about selling mine. The prices ranged from 9 to 20 thousand.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas