45 ammo costs twice as much as 9mmbecause there is twice as much lead, more powder, more brass, andthey are twice as heavy given the same number of cartridges so transportation cost more.

Like was said above any of the ones listed will be more than effective against a criminal provided you use proper ammo intended for such purposes. Keep in mind that you need to be familar with what ever you handgun youchoose so if the cost of ammo will keep you from shooting it often thenI strongly suggest the 9mm just for the simple reason that you will practice more and be far moreproficient with it. Flinging a bunch of big and heavy lead down range doesn't do you a bit of good if you couldn't hit the barn walls if you were standing inside the barn.