My daughter has 'Market Day' where each student has to make 10-15 of one type of item and sell it for 10-25cents each. They learn to make correct change, math, marketing (they make signs), and more. She's really excited. I helped make a display for the rings we made together.
It is made from an old thin wooden picture frame, 2 layers of cardboard and a cardboard stand stapled on the back. Bulk lace is stapled to the back and the stand to keep it secure and stable. A scrap of black spandex material is taped and stapled around the first cardboard. I love spending nothing and making something useful! The back isn't pretty, but it won't be seen.