There's no need to spend a lot of money on e-books for your e-reader. Most libraries now lend e-books for a variety of e-readers. I've boiled down the process for borrowing a library e-book for any Amazon Kindle e-reader device such as the Fire or Kindle app to six easier-than-they-look steps.
Each library Web site is likely different, but you should be able to browse best sellers, topic categories or search for specific titles or authors just like you do on Amazon. But libraries don't stock every e-book and only have limited copies of those they do have. As you can see, you can add yourself to a waiting list and be alerted when an e-book edition of your desired title becomes available.