All 8 current books in The Expanse series by James S.A. Corey on sale in the US. $2.99 for the first, $3.99 for 2-7, and $5.99 for the latest which came out earlier this year.
Kobo US
Amazon US
Highly recommend both the books and the show based on them (Amazon Prime). Near future space opera, but be warned there's some horror in the first book. (If you're a wimp like me, you could probably skip the Prologue and come back more prepared. It's a flashback which you don't realize the significance of until later in that first book. Definitely worth it.)