I got it made at http://www.murerase.com/ . Its 18x24 and cost approx $120.00. It did not include a frame. The cost includes a $35.00 art/setup fee and a $22.00 delivery fee. If I get anything else through them I do not have to pay the $35.00 fee again.
We make something similar for fire trucks to use for pump information . I did a different graphic for the Beast. They're polystyrene with a heavy dry erase laminate mounted on rigid magnetic sheet so they can stick them on the side of the fire truck, inside a door (or on the side of a cooker).
Here's a pic, you can see one of them on the right hand door.