For me, I go to the dollar store here in Philadelphia and buy the Sunbeam brand. Are they the best? NO. But they are good and certainly are a lot cheaper than the Energizers or Duracells! LOTS CHEAPER. For one dollar I get four button cells or eight AA cells. The WORST place to buy batteries is Radio Shack, although back in the sixties they were the price leader in the USA for batteries.
And note: I keep batteries sealed in small plastic food bags and place the bag in my freezer. I swear that that prolongs their life. - David Lyga