Sarah used on hers but I can speak to how I made this project less expensive...
WOOD: Sarah uses a larger piece of wood for her headboard that I did. I have a queen sized guest bed I'd like to create another headboard for so I decided to risk being short on wood and had the handy man at Home Depot cut a piece of 1/2" plywood in half for me so that I could squeeze two headboards out of one piece of ply. The final dimensions for our king size headboard were 24"x77". (If you decide to do this on your own, don't use anyone else's measurements. Measure your bed because they can vary.) The board pictured above drops only 2-3 inches below the mattress line but thanks to the sidearms you can't tell.
FOAM: If you've looked, foam can be crazy expensive. Some of the foam I saw was $60 a yard!!! I was not even close to considering spending that so I went to target and bought myself twin sized egg-crate mattress pad for $13. It wasn't thick enough to get a deep Victorian looking tuft which is good because that's not what I wanted. (
FABRIC: drop cloth. I think it was between $10-$20 at Home Depot. It was just what I needed and the color I wanted.
And that's that.