If you didn't do the recent Humble Bundle, or the Gateway Collection of six titles that was on sale a while back, or just otherwise have these, an omnibus of the second three books in Frank Herbert's Dune series is on sale in the UK for £0.99.
The Second Great Dune Trilogy (no false modesty here
) contains:
God Emperor of Dune,
Heretics of Dune, and
Chapter House Dune.
Kindle UK:
https://www.amazon.co.uk/dp/B07GXSQHKY
Kobo UK:
https://www.kobo.com/gb/en/ebook/the...t-dune-trilogy