The savings per box however large or small is easily and quickly calculated using an on-line reloading cost calculator, link below. Obviously the cost per box varies depending on the cost of components we each pay. Presently for me a box of 7/8 ounce 12ga reloads costs 75 cents less per box of 25 vs 1 1/8 ounce loading. Your milage may vary.
http://www.trapshooters.com/rlcalcadv.htm