A while back I posted on the Cricut MB how I used some recycled Priority Mail boxes to store my 12 x 12 paper.
Here are a couple of photos of one of the boxes. The measurements I used are shown on the Post-it notes.
Before Okie bought her Cropper Hoppers she had a lot of paper stored this way. After I was able to buy my Jetmax cubes this was the cheapest thing I could come up with to hold mine. I have since purchased several of the Cropper Hoppers but still have eight of these in my cubes.