Although this may be a little late to be of use right now, I thought I would share a possible source of free cardboard. I was at a local discount store and notice a cart full of red and pink cardboard display backing from the greeting card section that was being taken down after Valentine's day. I asked about it's fate and the card vendor told me it was headed for the trash. I explained to her about my hobby and my need for cardboard and she told me I could take what I wanted. It's about .5mm thick and most sheets were 100% usable with no creases or tears. As long as you don't mind pink formers the price is definately right. I probably ended up with about 50 pieces so it shouild last for a few projects. I guess I need to be there the day after Easter too.