I would suggest a Kindle Touch as you are not locked to
Amazon so you can shop around for the lowest price ebooks. There are a few other sites that I have found for dont require you to have drm when buying a ebook on a kindle.
Quiteuseful ebooks is a good place to find all the literature for adults. Or try another site for daily deals as
groupon.ie, this is the ireland websites so try your countrys site for specific deals for you. Or this
blog is useful for doing your research on the kindle.