Expensive, but...
I've seen non-prescription designer sunglasses, or just glasses/sunglasses FRAMES sell for that much (I wear glasses). Given, for what amounts to a few grams of weight, unless it's pure gold, I shouldn't be paying $300+ without lenses.
These are expensive, but for a good reason, it's new and interesting tech. Not some corp trying to r@pe it's customer's wallets for the bottom line (yet)