This guy has built a pro-quality condenser mic from a beer can and some other bits and pieces. Omnidirectional small diaphragm capsule, ruler flat freq. response from 100 Hz to around 15kHz, attached to the power supply by approx. 7 ft. of cable, fits most mic clips, and runs on a 9v battery. He’s built them out of Pabst Blue Ribbon and Schlitz, selling them from $15 to $51 on ebay. Thanks Tom! Link.
Pabst Blue Ribbon Condenser Mic Microphone