I make my own boards for fabric. I use foam board cut into pieces 5 X 6 for anything up to 2 yards. The measurements I use for larger quantities is 12 X 8. The larger size board is the foam board..or if I have it corrigated plastic from Home Depot.
Our Dollar Tree store has foam board for , you guessed it...1.00 a sheet. The corrigated plastic at Home Depot is located in the aisle with the cut glass and mailboxes. It is about 5.00 a sheet. It is well worth the price.
To cut it out..I just mark it with pencil..and use a 60mm rotary cutter.
Hope this helps you. I am a do it yourselfer.
Peace and Blessings,