The G-Tech Soundwave backpack is a great value. It features NXT flexible soft speakers and has a standard 3.5 m jack. This bad boy is powered by 3x AA batteries.

Available is the Soundwave in the color schemes grey/black and beige/brown for not more than $46.99 a real bargain even if there would be no sound(wave) in this backpack. The draw is that there are no integrated controls. All control come from the player. Well for under $50 can you complain? Thought so.