At least when you download free books from the library the author gets the royalties they are due, unlike buying cds from eBay which are ripping the author off.
I love my Sony eReader. It doesn't have wifi but I don't need it. It has built in memory and memory card slots so it holds literally thousands of books.
It will read Kindle books. Download books to pc, transfer them to the reader via usb. This means I have a fully backed up library on my pc in case something happens to my eReader.
I have had mine for 4 or 5 years, the Sony PRS 505. You can buy it nearly new on eBay for around £40.