I went to the hobby store and bought one of those plastic cases to store small thingamabobs (sorry for the technical terms) like buttons and what-not. Then I took a hot utility knife (just heated it with a lighter) and cut out the dividers till I had 3x4" areas divided--no reason this couldn't be done to 4x5" or whatever size. Later I will be drilling holes in it with a paddle bit then covering any sharp edges with a little epoxy. Total cost: $3 including epoxy