On the site I go on there offers of books of various genres of kindle books to download (500 or more) for a price you select from $8 to $35 .
I selected 560 scifi for $15 which came to £12 and also bought audio books (there is a kids audio books offer)
link to site.
Well worth it if you read a lot
click on the genre you want and you can usually get a list you can get in your selection and also pick your price you want to pay