Check out this lovely mechanical wooden coin bank by artist Christopher Blasius. When you turn the handle a snail emerges to grab the coin and pull it into its shell. The reverse side is covered in Plexiglass so the mechanism can be seen. Love those gears! Plans are available and the latter portion of this video shows you just what you'd be getting into if you decide to make one for yourself.
Here is where you can buy the plans for the mechanical snail coin bank.
[ Via the Spiel und Kunst mit Mechanik blog ]