Check your old emails offering you Sports for £20/month. Many of these codes don't expire despite what it says on the email. I have one that says "save over 40% and get behind the Three Lions" and it still works,
I have a sneaking suspicion there may be an offer in email or on the site tomorrow as after a blank Premier League last weekend for Sky and the distraction of the six nations, Sky has four decent premier league games and no rugby on the terrestrial channels.
Alternatively, wait a week or two for the F1 season offer. In the meantime get one of the day/week passes with 5 months of Sports on a smartphone.