A bunch of Amelia Peabody books by Elizabeth Peters are £2.99 each in the UK. Some have been at £2.99 for a while, and others are recent price drops. I love the UK covers for these.
Curse of the Pharaohs, #2
Kindle UK:
https://www.amazon.co.uk/dp/B007D1COEY
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B007D1COEY
Deeds of the Disturber, #5
Kindle UK:
https://www.amazon.co.uk/dp/B005E88KGO
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B005E88KGO
The Last Camel Died at Noon, #6
Kindle UK:
https://www.amazon.co.uk/dp/B007H989M8
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B007H989M8
The Snake, the Crocodile and the Dog, #7
Kindle UK:
https://www.amazon.co.uk/dp/B0080K3N4W
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B0080K3N4W
The Ape Who Guards the Balance, #10
Kindle UK:
https://www.amazon.co.uk/dp/B005E88CYE
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B005E88CYE
Also, the first book in the series,
Crocodile on the Sandbank, is semi-long-term at £1.99
Kindle UK:
https://www.amazon.co.uk/dp/B005E8832K
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B005E8832K