I don't have a Nectar card and I'm not going to buy anything where the Nectar price is cheaper. Doesn't this just expose which foods are a massive rip off? I think it might backfire on Sainsburys.
Things like that are not a massive rip off but are sold as a Loss leader to get you in the store to buy other things. My Nan used to call offers like that a "call bird". Nothing wrong with Nectar card either - you need that to use the scan and shop, you get special 'deals' and prices and you get points that equate to money off. I have a Tesco club card and a Mark's and a Waitrose card that work on the same principle. They all do it so if you shop in those stores, I think it would be foolish not to have one.