I didn't have bead bag pillows, or a foam pad/pillow to attach to the bottom (the material of my choice), but I did have foam pipe insulation. Pipe insulation is cheap, costing around $1.50 for 6'. I cut the pipe insulation into 18" segments
I could have spent more time trying to make the pipe insulation perfect, but why?
The final product is fully functional, and cost about $4 and 20 minutes of time to make 2.
My next production of lap desks will be made from whiteboard material. It will be suitable for multitasking. Maybe I'll also make it from ballistic materials. Parents and schools would eat that up.