Why is anything related to Thunderbolt so insanely expensive?
Because the market is currently very small - limited to people who bought a new Mac in the last year or so, and who actually need something faster than Firewire 800. Economies of scale are a huge factor in electronics pricing.
The first people being served by the market are video and graphics pros who were left up the creek by the removal of the ExpressCard slot from all but the 17" MacBook Pro. That's an even smaller market, and sellers can charge what they like.
But I can't remember the last time I paid more than $50 for a USB 2.0 or ethernet hub.
This isn't a USB 2 hub or an Ethernet hub, or an internal-SATA-to-eSATA cable. It contains Ethernet, USB 3, Firewire and eSATA controllers that that offer the same sort of performance that you'd get if they were built onto the motherboard.
If you just want to connect a mouse, keyboard and card reader then a $20 USB hub is all you need. If you want to add eSATA or an extra Gigabit Ethernet port, only Thunderbolt or USB3 will cut the mustard... and how do you add USB3 to your 2011 Mac?
This is expensive because the only other thing on the market remotely like it is built into a $900 monitor - and even that doesn't offer eSATA or USB3.
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