Four books in Lawrence Block's Matthew Scudder series are $1.99 each in the US right now, and the first one is semi-long-term at £1.99 at Kindle UK.
The Sins Of The Fathers, #1
Kindle UK:
https://www.amazon.co.uk/dp/B005XBUENY
Out on the Cutting Edge, #7
Kindle US:
https://www.amazon.com/dp/B000FC137C
Kobo US:
https://www.kobo.com/us/en/ebook/out...cutting-edge-1
A Dance at the Slaughterhouse, #9
Kindle US:
https://www.amazon.com/dp/B000FC11BK
Kobo US:
https://www.kobo.com/us/en/ebook/a-d...aughterhouse-1
The Devil Knows You're Dead, #11
Kindle US:
https://www.amazon.com/dp/B000FC11EC
Kobo US:
https://www.kobo.com/us/en/ebook/the...-you-re-dead-1
Hope to Die, #15
Kindle US:
https://www.amazon.com/dp/B000FC126O
Kobo US:
https://www.kobo.com/us/en/ebook/hope-to-die-1