$1911

On the site I always found people proposing to glue a kumihimo template on a piece of cardboard, but I always found that option a bit too flimsy on its own. Instead, I used a piece of clear plastic sheet, the kind that needs to be punched holes out to make transparent covers for books bound by a mechanical binder. I glued a piece of thin black cardboard on each side to give it a nice look, and then I cut out the shapes. It works impressively well and can be done on a budget

You could also buy thicker foam for a good price at a dollar store or craft shop as well.

Foam has a disadvantage though: Usually it's either too flimsy or too hard, and to cut it properly with the design provided on this site, it will leave poor edges. So you would have to invest in either an hot wire cutter or some foam cutting scissors, while layering plastic allows you to have thinner disks, of the sturdiness you prefer. It's all about the thickness and texture, personally I hate touching foam for its strange feel

Cut 1 from a sturdy notebook cover.