All, or almost all of GA Aiken's Dragon Kin series has dropped to $2.99 each or less at Kindle and Kobo US, just in the last few days. The titles at Kobo are discount/VIPable. Note that there have been a couple of omnibuses of these available on sale in the past, so check carefully before you buy.
I quite enjoyed about the first 2/3 of this series when I read it a while back, and the last few titles weren't terrible, just not quite as fun to me as the earlier ones.
For the Kobo link, you have to page down a few titles before the series starts, and both links may have a stray or two.
Kindle US:
https://www.amazon.com/kindle-dbs/en...SelectorHeader
Kobo US:
https://www.kobo.com/us/en/search?qu...&sort=PriceAsc