LightInTheBox offers the Uno R3 Basic Starter Kit for Arduino for $17.99 with free shipping. That's the lowest price we could find by $6. It includes the Uno R3 development board, mini breadboard, various resistors and LEDs, remote, and more.
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.