Three titles in the Pierre Chambrun series by Hugh Pentecost are $1.99 at Kindle and Kobo US, and also discountable at Kobo. Some have been on sale before, and these are Open Road/Mysterious Press titles, so check carefully before you buy! I read a bunch of these back in DTB days, and liked them, although I'm not really quite sure why. I think I liked the idea of the Beaumont Hotel as a city unto itself, or something ???
Birthday, Deathday, #8
Kindle US:
https://www.amazon.com/dp/B0096LJP00
Kindle US/Smile:
https://smile.amazon.com/dp/B0096LJP00
Kobo US:
https://www.kobo.com/us/en/ebook/birthday-deathday
Walking Dead Man, #9
Kindle US:
https://www.amazon.com/dp/B0096M15RA
Kindle US/Smile:
https://smile.amazon.com/dp/B0096M15RA
Kobo US:
https://www.kobo.com/us/en/ebook/walking-dead-man
Time of Terror, #11
Kindle US:
https://www.amazon.com/dp/B00FPX9DZU
Kindle US/Smile:
https://smile.amazon.com/dp/B00FPX9DZU
Kobo US:
https://www.kobo.com/us/en/ebook/time-of-terror