Have you tried the library? It's a wonderful building with many books one can borrow for free. (Unless one is forgetful and absent minded and racks up fees.)
My daughter downloads books from the Ohio Digital Public Library. I've not used it yet, but from what I've seen, New and newer books are available. Luke the physical library, the only requirement us a library card. If it weren't for the digital library, my daughter would have little use for her tablet, other than schoolwork, visiting the sites she uses at school and the occasional visit to PBS Kids, Nickelodeon and Disney, American Girl, FaithGirlz and other book/author sites.
Ask if there is something similar at your library.
There us also Gutenberg, which has free books and there ate also free books to download on Google Play.
Try posing this question in the Books and Authors section.