Here is how any vocalist or musician, maybe, can make their own secret safe for small items or rolled up money, in a cheap microphone.
Step 1: Dismantle Your Microphone, Kinda
You can get a cheap Philips microphone at Wal-Mart for maybe ten dollars. I only got mine for a 1/4 to 1/8 connector. Just unscrew the windscreen and pull the mic off, then you can safely roll up your money and tuck it inside, screw the windsreen back on, and enjoy.