Sabriel by Garth Nix (Old Kingdom Book 1) is currently $1.99 in the US and is also discounted in some other countries.
https://store.kobobooks.com/en-us/ebook/sabriel-1
https://www.amazon.com/Sabriel-Old-K.../dp/B000FC13MM
Since childhood, Sabriel has lived outside the walls of the Old Kingdom, away from the power of Free Magic, and away from the Dead who refuse to stay dead. But now her father, the Abhorson, is missing, and Sabriel must cross into that world to find him. With Mogget, whose feline form hides a powerful, perhaps malevolent spirit, and Touchstone, a young Charter Mage, Sabriel travels deep into the Old Kingdom. There she confronts an evil that threatens much more than her life and comes face-to-face with her own hidden destiny. . . .