Actually, the device the OP described exists. (Or as close as we'll see this decade.)
However, since pricing is a function of volume/demand, the pricing (as Mr Dulin pointed out) is anything but cheap:
http://www.http://www.engadget.com/2...-like-an-e-bo/
http://www.engadget.com/2010/02/12/b...eaper-still-1/
The current reality is that the center of gravity in ebook readers these days lies in recreational fiction. Mass market paperback-equivalents. (See: "rise of the $0.99 ebook".)
That is why Kindles and Nooks sell by the millions and everything else by the thousands and tens of thousands (at best).
And why no manufacturer really bothers with academic pdf readers.
The money is in the books, not the hardware. Especially under the Oligarchs' Agency Model.
The features that some people seem to consider valuable (pdf viewing, touchscreens, annotations, content generation) don't sell ebooks. (Or readers)
Wireless connectivity, especially when tied to dedicated ebookstores, does.
It is going to be a *long* time (aka, 2015+) before the recreational reader market brings technology costs down (single-chip readers, LCD-level eink pricing, dirt-cheap digitizers) to the point that the academic market niche *might* become profitable as a pure hardware play. Before that, we will more likely see walled-garden etextbook readers (probably from B&N, maybe Amazon) and they won't be cheap. (C.F. Kindle DX, PB903, IRex)
Until then, anything with academic-level features and content creation capabilities will be a computer, not a reader.
The best hope lies in the ADAM tablet from Notion Ink or future Pixel Qi Tablets.
http://www.crunchgear.com/2011/01/17...ere-its-going/