A couple of titles in the Blotto & Twinks series by Simon Brett have dropped to $3.99, which is the upper edge of where I post, but this is a fun series IMO (somewhere upthread I likened it to Rhys Bowen's Lady Georgie series with some PG Wodehouse mixed in) and, with the exception of the first-in-series, titles in this series don't seem to drop below $3.99 much. So, here you go:
Blotto, Twinks and Riddle of the Sphinx, #5
Kindle US:
https://www.amazon.com/Blotto-Twinks...dp/B00OGUPD9S/
Kobo US:
https://www.kobo.com/us/en/ebook/blo...f-the-sphinx-3
Blotto, Twinks and the Heir to the Tsar, #6
Kindle US:
https://www.amazon.com/Blotto-Twinks...dp/B00TE8KA68/
Kobo US:
https://www.kobo.com/us/en/ebook/blo...-to-the-tsar-1
In addition, if you missed the first title when it was on sale for $0.99 a while ago and you would like to give the series a try, it is still only $2.99, which is not too bad.
Blotto, Twinks and the Ex-King's Daughter, #1
Kindle US:
https://www.amazon.com/Blotto-Twinks...dp/B00OGV2JK8/
Kobo US:
https://www.kobo.com/us/en/ebook/blo...g-s-daughter-4
Finally, the second title in the series has been at $3.99 for most of 2018.
Blotto, Twinks and the Dead Dowager Duchess, #2
Kindle US:
https://www.amazon.com/Blotto-Twinks...dp/B00OGV2JHG/
Kobo US:
https://www.kobo.com/us/en/ebook/blo...ager-duchess-4
Note: Be careful of multiple editions - some or all of these have two versions, only one of which is at these prices...