Get thee to thine Costco, to thine safeway, to thine ethnic grocer and look at prices.
Big boy purveyors like to lump prices into volume, do "X" amountof volume and you fall into price category 1, "Y" volume and your into price category 2 etc.
If big box stores are cheaper, and in an amount that makes financial sense to spend 2 hrs/week buying stuff like dairy, pop, and drygoods, thenit's time to have a lil' chat with the purveyors and ask them why you shouldn't go to the big box stores.
For my part, I've had far better pricing buying coffee froma coffee supplier, poultry from a poultry supplier (even throws in a cse of bones for every $200.) beef from a beef supplier, pork and charcutierie from a German guy, and produce from they guy down the street, car better pricing on "case lots" for stuff like tomatoese, onions, pots, and staple fruit and veg.
One of my big "sayings about life in general" goes something like this:
-Giants play best with other giants--not saying we all can't get along--but when giants play with other giants, neither goes home feeling like they got shi**y deal.