Walgreens.com (and maybe in store?) has 4-packs of AA or AAA alkaline batteries for $1.00. Use WAG10 at checkout to get 10% off to make these $0.90 per pack. Minimum order size for store pickup seems to be $10.
AA: https://www.walgreens.com/store/c/walgreens-alkaline-supercell-batteries-aa/ID=prod6091756-product
AAA: https://www.walgreens.com/store/c/walgreens-alkaline-supercell-batteries-aaa/ID=prod6109689-product
AA: https://www.walgreens.com/store/c/walgreens-alkaline-supercell-batteries-aa/ID=prod6091756-product
AAA: https://www.walgreens.com/store/c/walgreens-alkaline-supercell-batteries-aaa/ID=prod6109689-product