Sorcerer to the Crown by Zen Cho is in the monthly sale at amazon.co.uk. The price sale is available at amazon.fr and probably for all Europe. I can't see the price in £ but it's 1.19 € at amazon.fr.
https://www.amazon.co.uk/Sorcerer-Crown-novels-Book-ebook/dp/B00UXKJ0GM/ref=sr_1_370?s=digital-text&ie=UTF8&qid=1543641719&sr=1-370