Full credit to golfer2007 for mentioning this on the Canadian PSN thread.
Until Dawn is one of the few games cheaper on PSN US than Canada. Using PCGameSupply's exchange rate of $15.78 to £20, $9.99 equates to £7.88.
Furthermore, you can use the PS+ trick to save a further 10% (from the base price of $19.99). That'd make $7.99, or £6.30.
PS+ trick (once per account): Sign into your US account and attempt to upload a save file to online storage. You'll see a message saying this is a feature of PS+; here's two days free!