there are a few factors that make food more expensive in BG, they have 20% VAT on food to start, then there's import cost and a lack of competition to the big German chains. probably other factors like the economics of scale and things. how much of it is related to the price policy of the stores themselves, I'm not sure.

logically, a locally produced stick of butter or egg shouldn't cost more than a german one though, especially when wages are here are way lower, along with operating costs and everything else