I bought a plastic placemat from Walmart for $1.58 plus tax. I used Velcro that I had on hand, as well as some felt so it was softer around the neck. If you need a cone collar for a cat or a small dog, you should definitely make one of these! It only took about an hour to make!
I used a plastic protector for the neck hole and a pizza pan for the larger circle; plus my sewing machine and a heavy duty needle. For specific instructions, leave a comment and I'll put together a tutorial. :)