Seeing as the controllers are almost a handheld on their own, I'm not really that surprised they cost so much.
Except without all those pesky CPUs, GPUs, memory, etc. They've got a screen, sure, but they're still totally dependent on the console to do anything. This does seem like a lot. I would have guessed more like $100.
On the other hand, almost all console accessories are overpriced. That's just how things are in this industry.