The first
Dorothy Must Die book is on sale for $1.99. It's a publisher promotion (book 2 comes out in 2 weeks), so it should be valid anywhere in the US. I know
Amazon,
Kobo,
Google Play, and
B&N are honoring the price.
I should note that there are three prequel novellas (all before the first book), and the first of those (No Place Like Oz) is $1.99, but I'm not sure whether that's a promotion or not.