what are some dirt cheap, small e-ink displays?
I had, for a brief period of time, considered the idea of tinkering with the eink displays; and followed up with e-Ink Corporation.  They are the folks holding the eInk IP.  They referred me to PrimeView, which is a well established LCD manufacturing company.  (And as I googled to do some fact-checking, it turns out PVI has now acquired EInk.)

I was able to talk my way into some datasheets and pricing data.  I'm afraid it doesn't look good for the average tinkerer.  They were quoting $ 200.00 per piece for the display.  and 4.50 per piece for the controller (in sample quantities).  The panels were quoted at  60.00/pc for production volumes. Of course, that latter quote would depend on the volume - and I suspect Amazon gets much better pricing!  (BTW, this was for the 6" panel, quoted around December 2007)

If you are really serious about it, they did offer their development kit for around $3,000.

Given that the technology is still relatively new and much of the key technology (versus the enabling technology) is under a lot of patent protection, it'll be a while before we'll see commodity (generic) e-ink displays.