But a lot of e-Readers tend to be quite expensive.

Have I missed something? If you are ok with a basic e-reader (not high end) you can easily get one for 100 to 150€. Only the cheapest smartphones cost in this range. So they are NOT expensive in relation to smartphones. Especially, when you consider all the people having iPhones or other expensive phones, ranging from like 500€ to over 1000€.

The tolino shine color is 150€. I don’t know about jailbraking it, though it works perfectly fine offline with placing ebooks via USB, without any changes.