LightInTheBox offers the OEM Waterproof Bluetooth Speaker in several colors (Blue pictured) for $5.99 with free shipping. That's the lowest price we could find by $6. It features a microphone, suction cup, and volume control.
Note: This item ships from China and may take two to five weeks to arrive. Uncheck "Add Shipping Insurance to your order" during checkout to remove the 49-cent fee.