I bought a knock-off one on eBay for $16.99 - the one with red wires that you see being sold for cheap. Unfortunately, it doesn't work very well so my only other option is the official Apple one. I'm hesitant to buy one, however, because the reviews on Apple's own website are pretty terrible. Strangely, the reviews on Amazon are great. I can't understand how the reviews can be so different for the same product. Does anyone own one and can tell me how well it works? Also, does it require a power source for it to work? The one I got on eBay required it to be plugged in with an AC adapter.