The elevation in price is less location and more whether you're able to buy in bulk. With careful rotation discipline and a handcart it's achievable on foot though, although clearly more convenient with a car and a nice wide lot.
Off the cuff I'd say I save about 20%, and buy a few hundred pounds per trip. Probably saves us amongst a family in the vicinity of $1000/yr. This same concept extended to all other non-food consumables.