Books 2-8 in the Ruth Galloway series by Elly Griffiths are part of today's US Kindle Daily Deal, matched at Kobo US. They range from $1.99 to $2.99 each. I've quite enjoyed all of the titles I've read in this series.
Kindle US series link:
https://www.amazon.com/gp/product/B0...ies_rw_dp_labf
Kobo US series link:
https://www.kobo.com/us/en/search?qu...&sort=PriceAsc
Sadly, the first book in the series is $4.99 right now, but it does go on sale pretty often. Also, there is a free novella available, which shows up on the Kobo series page, but not on the Kindle series page. Here's that link:
https://www.amazon.com/Ruths-First-C...dp/B00AFDUN72/