Since they're now pub by Open Road in the US, lots and lots of titles in the excellent (IMO) Gideon Oliver series by Aaron Elkins have been on sale before at various prices. However, here's a particularly good deal if you've never tried the series, and like reading in order - the first four titles in the series are on sale in an omnibus for $3.03 at Kindle US. Assuming you don't have any of them, this works out to $0.76 per book, which is about as good as you're going to get without freebies, which Open Road doesn't do often (other than their freebie-thon around the holidays a couple of years ago). I actually don't think the first two titles are are a great representation of the rest of the series, although they do give some good background, and are not bad at all - just not among my favorites, and they don't showcase Gideon as "Skeleton Detective" as much as the later titles. But I love the next two, especially
Old Bones, since I am a push-over for mysteries set in France.
The Gideon Oliver Mysteries Volume One: Fellowship of Fear, The Dark Place, Murder in the Queen’s Armes, and Old Bones:
https://www.amazon.com/dp/B07CMDXW7X