Several early books in Laurie R King's excellent IMO Mary Russell/Sherlock Holmes series are £1.79 each at Kindle UK, sadly not matched, at least as of now, at Kobo UK. And the first book in the series has dropped to £0.99.
The Beekeeper's Apprentice, #1
Kindle UK:
https://www.amazon.co.uk/dp/B006WB7JOG
A Monstrous Regiment of Women, #2
Kindle UK:
https://www.amazon.co.uk/dp/B00HUTVW5G
A Letter of Mary, #3
Kindle UK:
https://www.amazon.co.uk/dp/B00HUTVW6K
The Moor, #4
Kindle UK:
https://www.amazon.co.uk/dp/B00HUTVWE2
Justice Hall, #6
Kindle UK:
https://www.amazon.co.uk/dp/B00HUTVWD8