Books 2 & 3 of
Mercedes Lackey's
The Founding of Valdemar trilogy are 99¢ each at various US retailers.
Into the West (Book 2):
https://amazon.com/dp/B09GVZTGXV
https://www.kobo.com/us/en/ebook/into-the-west-7
Valdemar (Book 3):
https://amazon.com/dp/B0BY7TCLSF
https://www.kobo.com/us/en/ebook/valdemar-1
Into the West has been $1.99 in the past (as has book 1,
Beyond). To the best of my knowledge, this is the first sale on
Valdemar.