In my household, we love blocks. We are pretty hard on them too!
I have purchased cardboard blocks. They work pretty well, but can get expensive. However, since we are so hard on our toys...they get messed up. I've come up with a solution to add to our collection, while making use of what would be waste items. I saved cardboard food boxes. I stuffed them full of shredded paper and crumpled newspaper. Seal closed with packing tape or hot glue, and you have a great toy. Pictured are pasta, bacon and easy mac boxes. I've also used frozen waffle and cereal boxes. My kiddos use these to build castles and towers...but these are versitile, because the kids use them in the kitchen area to cook and grocery shop.