Popslate is pretty cool, I saw it at MWC 2013 in February of 2013. I guess it never took off because it was too expensive. Guess what - it's gotten more expensive ($129 now). Bummer.
I came here to wonder about the price, and there's the answer. It's a pity that eInk is a great technology that remains horribly expensive. Not sure why; manufacturing yield? Rare inputs? Small volumes?
I recently bought a replacement 6" E Ink screen for my kindle at it cost $30. This device has a 4" screen, not sure on the relative resolutions.