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It's expensive because there's a lot going on in that cable. Lightning doesn't have a native video out, so the cable is taking a data stream and using it to produce its own video signal. It's almost like a little primitive version of an Apple TV in that cable! This is why it is hard to find a third party alternative. Dock Connector to HDMI is a straight cable connection with no complex processing which is why the cable was cheaper and third party options available. However, on eBay or at a local electronics store you may find used or open box ones for less.
 
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