Three JK Rowling "Hogwarts Library" books, which are tie-ins to the Harry Potter series, and are usually mentioned (or even essential elements) in the main seven books, have dropped in price right now, both in the US and the UK.
Fantastic Beasts and Where to Find Them (not the original screenplay)
Kindle US, $1.99:
https://www.amazon.com/dp/B01LYBG60A
Kindle UK, £1.99:
https://www.amazon.co.uk/dp/B01LZY70SV
Quidditch Through the Ages
Kindle US, $1.99:
https://www.amazon.com/dp/B01F3ET2QU/
Kindle UK, £0.99:
https://www.amazon.co.uk/dp/B01F3ET2SS
also at Kobo US, $1.99:
https://www.kobo.com/us/en/ebook/qui...ugh-the-ages-4
The Tales of Beedle the Bard
Kindle US, $1.99:
https://www.amazon.com/dp/B01F3ET2SI/
Kindle UK, £1.99:
https://www.amazon.co.uk/dp/B01F3ET2RE