Looking through this month's SF sale titles at Amazon, it looks like they're doing something a little different. Instead of putting book 1 in a series on sale like usual, many of the sale titles this month are the latest available title.
Queen: A Chronicle of the Sibyl's War (book 3) by
Timothy Zahn is on sale for
$2.99.
Knight (book 2) hasn't been below its normal price of $8.99, yet book 3 goes on sale.
Other not book 1's on sale:
Spaceside (Planetside Book 2) by
Michael Mammay is on sale for
$1.99
Book 3 will be out in December.
Conventions of War: Dread Empire's Fall (Dread Empire's Fall Series Book 3) by
Walter Jon Williams is on sale for
$2.99
The Accidental War: A Novel (Praxis Book 1) by
Walter Jon Williams is on sale for
$2.99
Book 2 will be out in December.
There are more, but generally not from authors I'm familiar with.