Namco Bandai Games offers Steam downloads of Dark Souls II for Windows for $19.47. That's $6 below our July mention and the lowest price we've seen for this action role-playing game. (It's a current low by $21.)
Also available are Steam downloads of the Dark Souls II Season Pass for Windows for $16.22. That's the lowest price we could find by $9. It includes the Crown of the Sunken King, Crown of the Old Iron King, and Crown of the Ivory King DLC packs.