Walmart has the Disney Frozen Light-Up Message Board on clearance for only $5.83 right now! (Reg $14.99) The built in light in this board makes the written messages glow brightly, and it includes a marker. It also has a magnetic back, which allows it to be mounted to the refrigerator, inside of a locker, or most other metal surfaces.
Pick up is free, or you can have it shipped for free with a $50 order.