Step 1: Materials
In addition to what you see here, you need:
a soldering iron
You will notice in most of the following instructions that I only used two magnets. This is because during my initial build, I thought that two would be sufficient, and it was only when the whole thing was built and photographed that I discovered that they were not. Rather than start over, I simply used my Dremel to insert another two magnets, and the final design you see on the first page was born.
Depending on how many materials you already have, this should cost less than $30 for the whole project.