This deal has ended.
Best Buy now has Rock Band 2 for either PlayStation 3, XBox 360, or Nintendo Wii on sale for just $19.99. This is just the gaming software and does not include any of the instrument controllers. Note that some are backordered and may take up to two weeks to ship. Shipping adds $2.99, in-store pickup is free where available, and sales tax is charged in most states.