I got a catalog this weekend that features some plastic 9mm ammo that can be used for training out to 50 feet. It costs about 4 cents per round. It's not powerful enough to cycle an action. It seems like an interesting option for those wanting to shoot cheaply. You can't buy conventional ammo for this price. It's some kind of military training round from NATO.
Another thing: Those 45ACPs sure are a lot bigger to carry than 9mm's I can see why the military would want a smaller lighter round for cost and logistical reasons. I'd rather carry 100 rounds of 9mm than 100 rounds of 45. But I'd feel a lot better about it if the 9mms was expanding defensive ammo.