I imagine you can also find these at AC Moore or Hobby Lobby, or other such stores. They are $1.00 each at Michael's here in Virginia. The ones on display had little fake flowers behind the glass. Basically, the lid is thick, and has a removable panel on the back of it, inside which you can put whatever you want - then seal it up (folding prongs hold the panel in place) and voila: a simple and easy project. The toughest part of the whole thing was cleaning the glass after the wood stain got on it.
I used MinWax gel for the wood stain, Feibings blue for the leather, and a new concho I got from Tandy. I was thinking over a reasonable asking price, and am going to start them at 15.00.