GameStop offers Batman: Arkham Knight for PlayStation 4 or Xbox One for $9.99. Opt for in-store pickup to avoid the $4.99 shipping charge. That's tied with our Thanksgiving day mention of a shipped unit and the lowest total price we've seen. (It's also the best deal now for either platform by at least $6.)
Toys"R"Us offers it for the same price for Xbox One via in-store pickup.