Store brands account for about one of every four products in a supermarket— and they're branching into niches that lack national-brand competition: balsamic vinegar, for instance, or chocolate-covered raisins. Their popularity is understandable, considering that they typically cost 15 to 30 percent less than name-brand counterparts, according to an industry expert. As the table below shows, some of the store brands we tested were more than 30 percent cheaper. The name-brand premium is largely the result of advertising and promotional costs that are passed on to consumers.