I thought this was a bit of a bargain. They had stickers on them for £5 each but when they got scanned at the checkout they came through at half price! That's 120 full days of neglecting your social life and eating nothing but crisps.
This was at WHSmith in Exeter, there was only one other one left on the shelf at the time but I thought it was worth posting anyway in case it's nationwide.
Actually I could have put the deal as 1 card for £2.50 as it doesn't look like it was dependent on me buying 2. Ah well.