A 08-09 cayenne is around $30-35k around here.
But I think I'll get the Mustang, a probably the cayenne or a explorer sport later.
That certainly is lower than the expected price range on kbb.com for a turbo version of a 09 Cayenne. I think that the price range that you indicated above is in the range indicated on kbb.com for the non-turbo version of the Cayenne with roughly 50,000 miles (so maybe the one that you saw advertised is a relative bargain). For reference, the link below should take you to the kbb.com page where you are able to select between the different Cayenne models, and specify the number of miles on the car: Kelley Blue Book
I agree with scott9050, slorydn1, and Apollo1 that if you can afford a GT (or better yet a GT premium) while keeping the truck, that is probably the best course of action than the V6 that I suggested.