Wheel Well Cover
 

I've lost the wheel well cover for my 2000 Mustang on the driver's side..you know, the hard plastic moulding that is bolted to the body that covers the air intake and other components....

Anyone know where I can get a new one or a used one, or even an after market one? I don't want to find one at the dealer, because we all know they sell stuff at a hellacious markup.

You can go to the parts desk forum:
https://mustangboards.com/parts-desk/

Start a thread and ask Randy to quote you a price on one, as long as it isn't discontinued. :)

Yea go to the parts desk, btw how did you actually lose it? Did it fall off while you were driving? That wheel well cover is pretty big and if it fell off while you were driving, you should check the strut and spring assembly to make sure it didnt damage anything.