An iPad-sized, Kindle-like reader would be a godsend.
The premium is not really high just from them having to spend particularly much. Either they make very nice margins on it, or it's really that expensive to get a screen that size.
And that would be a wrong guess. Eink readers with wacom styluses are not particularly new (e.g. Hanvon, onyx etc.). The remarkable 1's "claim to fame" was a greatly improved latency compared to these, i.e. to be much better than what you describe.
Back in the days of the C64, it was normal to have sub-frame average latency with +-0.5 frames jitter, due to low-level control that prevented artifacts when drawing directly to the framebuffer.