eReaders, even ones with epaper screens, are getting cheaper and cheaper. There's at least one model with a 4.3" E-ink screen which is going to sell for $64 in Europe, but that's not the cheapest one I have found.
No, that honor belongs to a refurbished Pandigital Novel eReader. This device has a Sipix screen, Wifi, 2GB of storage and card slot, and today you can find it for $20 on 1SaleaDay.
Pandigital is probably regretting having ever released this ereader, but their loss is your gain.
This device launched back in 2010 with a retail of over $100 when new. I didn't think it was a good value then due to the poor quality screen (grayer than the original Kindle) and otherwise unremarkable features, but now I think it's great value.
I'm tempted to buy a dozen just to use them as coasters. Or I might give them away to hackers in order to encourage them to come up with clever ways to use them.
In any case, I think this is a great value. Go buy a couple for your kids.