I just purchased a roll of black car carpet from an auto parts store. I did the whole cargo area with it. Mine had faded to brown from the sunlight since this area receives the most sunlight. It was easy to do. I just used the old pieces to trace on the new carpet. It cost me around 50$.
Oh, and yes, the plywood piece is carpeted like Adam said. There should be black trim pieces on the outer edges of the plywood.