Home depot sells that board stuff you're looking for. It comes in 4' x 8' sheets, as well as 4' x 4', and 2' x 4'.

One side is rough, the other smooth. I'm not sure what it's called. It looks like a dense cardboard...but it's stronger than cardboard but not as strong as real wood.

Just use 3m adhesive and spring clips to hold the fabric/vinyl in place until the glue dries. Very easy. I did the entire interior of a car for less than $100 in materials, board, glue and vinyl included, and it only took one day. Aftermarket price was $1000 for the entire interior.