My point was not the cost,
per se, but taking the time to make sure that your shottie "likes" a given load.
It may be the same on the spec sheet, but there are subtle differences that may make a difference in performance.
Most of my shooting is Trap - I'm not good enough for brand of ammo (or shottie) to make a perceptible difference, but the top-level shooters have found the "ideal" combo.
If I miss a bird, my score has not changed significantly; the shooter in the running, or a hunter with a turkey lined up has a bigger investment.
Winchester AA ammo sells for ~2x the price of ammo that has, nominally, the same shot charge and velocity. I shoot the cheap stuff.