Wow those are really neat, but pricey for sure! I noticed they are made from wool felt. If its 100% wool your looking for its harder to find. You can find wool/rayon blends and then the polyester felt sheets at crafts stores. I did find 100% wool by the yard at JoAnn for 14.95/yd in a natural color. All these felts are not as sturdy as the felt in the photo looks, I've never seen any for sale that thick. So I was thinking another choice would be to cut out 5 thin cardboard squares, and sew 2 pieces of felt over each one (cardboard in the middle), then sew them all together into the box shape. You'd need to be sure to make the fabric edge around each square wide enough so that you can easily sew them together. I
think this might work, though maybe the red-cross shaped mentioned above would be better than the 5 individual pieces.
I like this felt box idea so much I might have to try it myself soon! If I do, I'll let you know how it goes!
I think you can do it!

Go For it!
Maybe try the first one with the cheapy-felt so you don't have to worry about messing it up!
Good Luck!