I took the plunge and went to the Container store. This is a dangerous place for me, along with bookstores and hobby shops. At one point, I had a handful of items in my hand, but I walked out with just one item (for my scrap stuff). It's a box from a company called Livinbox. This is the Stationary Organizer and it was only $9.99. Double-stacked, I can fit up to 36 SU stamp pads in there. These are supposed to stack on each other, but I'll worry about that when I fill this up. :)
Below is the label on the box:
I think I am at 30 SU stamp pads, so I have room to put my other stamp pads if I want to.
There was another one available for 8.5x11 paper for $14.99, but this one had a deeper tray. I think this would work well for rubber stamps as well, but I am debating on whether or not I want to unmount those.