Green Man Gaming offers Steam downloads of Warhammer: The End Times - Vermintide for Windows for $9.79. (Sign in to get this price.) Coupon code "WINTER10" lowers it to $8.81. That's $3 under our mention from a month ago and the lowest price we could find by $6.
Of note, the Collector's Edition is also available for $14.57 before the above coupon, $13.11 after.