Check out Rockauto. I ordered the rear portion of the carpet for my 04 project suburban a few months ago. The mass backing option was more, but $100 more. My original had the foam backing, but it was pretty thin and dingy so I took that out.
The fit was okay, I just had to lay out in the sun so it would conform better to the rear tire humps. I will probably replace the front portion from the same place in the near future.