That almost makes me want to buy a 9mm because .45s are too expensive to feed.
One of the biggest reasons I own a 9mm. Even casting my own bullets, 9mm uses a bit more than half the lead. Lead can be a significant expense, if, like me, you are setting up a run of several thousand rounds. My 9mm rounds cost about 7.5 cents per round, .45 ACP would run about 11 cents per round due to increased powder and lead tests.
In terms of cost per box, I can load 9mm for $3.75 per box, while .45 ACP would cost me $5.50 per box. That means that My cost per thousand is $75.00 and $110.00 respectively. I do not think that I have ever done a production run of less than 4k rounds - for which the cost difference is $140.00.
These figures do not take into account the difference in the cost of brass, even once fired brass. I was able to buy great many empties at a range that sold brass at $3.00/lb. Again, .45ACP brass is much more costly.