Try ePub books from your local library
I would keep away from the expensive ereaders. I was given a KIndle, and it is great, but I am an adult with a disposable income. I bought my wife a HipStreet ereader, which is backlit and very inexpensive. Unfortunately, she cannot readily download books from the web onto it as it does not have an internet connection. BUt books can be readily obtained through many sources on the web for free. You just need to download them onto your desktop or laptop, then transfer them through a usb connection. The HipStreet ereader will read many different formats, but the most versatile is epub books. Download a free program called Calibre, and it will manage all of your library of books, plus much more.