I spent an afternoon putting this together as my first test project, designed to be printed with i.materialise. It should be pretty cheap to print (around $40 unpainted at 60cm), and the mechanical interactions are relatively simple, so if things are too tight you can simply sand the areas down a bit. Also, I made the walls rather robust so you could shrink it (even more!) if you wanted to. The default dimensions are 20mm x 20mm x around 2mm (about the size of a 1yen coin, or a quarter).
It has twenty rollers that are designed to be half-painted to denote poison between you and your opponent, and space to hold the rollers (or other objects that are 1mm in size at default dimensions) inside it.
The surface of it is rather plain, you can paint it if you like, but I also included the source file so you can create your own relief design on it as well.
