Originally Posted by QuiltE

There are different weights/qualities of Coroplast, so your price comparison may not be apples-to-apples!

Sign shops might give you a better pricing for offcuts that are in their scrap bin.
You might even get a variety of colours to have some fun with. (think -- colour coding representing their contents!)

You can usually buy it in Staples.
I've even seen it in some dollar stores!