There I was able to get large blue and black 2" binders at a deal. I negotiated from $3 each (at Staples they were about $12-$16 each) to less than $2 each. Some vendors had plastic sheets to store your blackline masters, plastic crates that would be perfect for the puppet centre, and Tupperware ideal for manipulatives.
So before heading to the regular teacher stores, try your local markets. It may take longer to find the items you need, but you will save a lot of money and we know how much we spend in the classroom already.