A five-foot Ethernet cable might run you about $20 at Best Buy. Less if you shop around on-line or get a bargain-basement cable. A cheapo cable is more likely to fail, but once you get up to a decent quality Category 6 cable, a cable is a cable is a cable.
But the folks at Denon actually have the gall to charge $499 for their AK-DL1 "proprietary ultra premium Denon Link cable". It's got all the bells and whistles: even "signal directional markings are provided for optimum signal transfer." (Presumably the electrons read the markings to figure out which way to go, because moving under a voltage is just so out of style.)
Worse is that there are people who would buy this, the same sort of "audiophiles" who buy Monster cables and Brilliant Pebbles
More at Wired's Gadget Lab.