Xbox currently has Batman Arkham Knight Premium Edition for £29.99 on the UK store. But, on the Canadian Store it's currently £13.82. If you don't already have the game, now is the time to pick it up. This does include the season pass.
If you already have the game then the season pass is £6.92 ($19.99) on its own.
Use this link to get some credit to the purchase easier:-https://www.microsoftstore.com/store/msca/en_CA/pdp/Xbox-Gift-Card-$25/productID.286521400