I LOVE the Linda Castillo "Kate Burkholder" series.
I have the Kindke unlimited. I don't feel it's worth the $10/mo.
I don't know where you're located but get a library card and get ebooks from there. You can download them onto your kindle, Nook, Kobo or cell phone. Many libraries get the newest books the day they come out. Unfortunately, there's always a long wait list. I scan my libraries numerous times per day to see when they add new content and try to be the first to reserve books when they add them to their site.