I know this is gonna sound weird, but why not get a nice .22 revolver? They are always more accurate than a semi because the barrel is fixed. Plus they are WAY less "finicky" with .22 ammo than a semi. This is sound advice for times like these when you often have to shoot the ammo you can find on hand, rather than the ammo you would like to shoot. I have a decent Smith and Wesson 9 shot revolver in .22 and a Taurus revolver in .17HMR. Talk about fun with rimfires. Plus they never fail to fire, fail to eject, stovepipe or any other foolishness.
As said before, .45acp ammo is quite expensive for any kind of volume shooting. Not much off $30 a box, even at Canadian Tire. Unless you can find one of those deals like at Can Ammo where you get a pistol and a shyteload of ammo.