Three fairly recent price drops to £1.99 at Kindle UK in the Rina Lazarus/Peter Decker series by Faye Kellerman.
Predator, #21:
https://www.amazon.co.uk/gp/product/B00ALKRZ52/
Cold Case, #17:
https://www.amazon.co.uk/gp/product/B002RI9QQC/
The Theory of Death, #23:
https://www.amazon.co.uk/gp/product/B00Y7KGUQC/
In addition, three others have been at the same £1.99 price for a little while.
The Ritual Bath, #1:
https://www.amazon.co.uk/gp/product/B07CMM6TT1/
False Prophet, #5:
https://www.amazon.co.uk/gp/product/B00FIUO8SC/
Grievous Sin, #6:
https://www.amazon.co.uk/gp/product/B00FIUO8S2/
And on a side note,
Grievous Sin is also priced at $1.99 in the US right now.
Kindle US:
https://www.amazon.com/gp/product/B000Z4JQN8/
Kobo US:
https://www.kobo.com/us/en/ebook/grievous-sin