BOM for a color eink about 35$ all together for a mass produced quantity of one, delivered anywhere (until tariffs).
Assumed quantity of customers, millions? Its so cheap that governments could give it out to schools, one eink ebook per child, cheaper than one year's worth of school books anyway.
Assuming it's that simple, do you have an alternate theory as to why e-readers in this range are not more common?
I definitely agree that selling hardware at cost (or at a loss) in the hopes of turning a profit off of content sales is an extremely risky strategy. Many companies try that approach, few succeed.
But if you price it like a typical consumer product and sell it for ~1.5 * BOM (i.e. ~$50 retail price on $35 BOM) then you don't need anyone to buy books because you can survive off the profit from the hardware alone. And because I believe that a $50 ereader would sell well, I don't know why they are not more common if it really is possible to build and assemble a mass-market ereader with a $35 BOM as the prior poster claimed.