Check out 1aauto.com. I bought a replacement and thought it was better in thickness and quality in carpeting and padding than the dealer. Im pretty sure it was cheaper too.
You can also get a rubber/vinyl replacement instead of carpet.
If you get a replacement, just remember to let it sit out for a day in order get the molded form back. Also, when putting a new carpet in, just cut a little bit at a time, you can always take off more.
Its also a get time to do a sound deadener in the cab, it makes a HUGE difference.