Bridge to Terabithia is a Newbery Medal-winner by Katherine Paterson. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US:
https://www.amazon.com/dp/B001UFP6JY
Kindle US/Smile:
https://smile.amazon.com/dp/B001UFP6JY
Kobo US:
https://www.kobo.com/us/en/ebook/bridge-to-terabithia