I bought a used 2001 X5 in great condition. One problem. The fan for the AC/heat does not work. There is no air movement even with the dial on full blast. I tried replacing the fuse with no luck. Heat comes out, but only when driving at highway speeds. What might be the problem and will it cost a fortune to fix?

Very common on X5's, 5 series and E46's. Your a/c blower motor final stage needs to be replaced. I believe the part costs between 100-200 hundred dollars (don't quote me on that) and shouldn't be more than 1.0 hr for labor and diagnosis. Very easy component to replace. Good luck. :)