The first four books in JD Robb's Eve Dallas/In Death series are on sale in the UK, with the first one free, and the next three at £0.99 each. Not on sale in the US, at least as of now.
Naked in Death, #1
Kindle UK:
https://www.amazon.co.uk/dp/B003MQM7B4
Kobo UK:
https://www.kobo.com/gb/en/ebook/naked-in-death
Glory in Death, #2
Kindle UK:
https://www.amazon.co.uk/dp/B003O86FL8
Kobo UK:
https://www.kobo.com/gb/en/ebook/glory-in-death
Immortal in Death, #3
Kindle UK:
https://www.amazon.co.uk/dp/B003LPULVO
Kobo UK:
https://www.kobo.com/gb/en/ebook/immortal-in-death
Rapture in Death, #4
Kindle UK:
https://www.amazon.co.uk/dp/B003LPULX2
Kobo UK:
https://www.kobo.com/gb/en/ebook/rapture-in-death