At this point, if you cast bullets 45 ACP might actually be cheaper to shoot than 9.

All pistol calibers are essentially $0.60 a shot these days new, large pistol primers are easier and potentially cheaper to get than the small ones due to demand, and powder charges in the two rounds are about identical.

The biggest different though is pressure. 45ACP as a low pressure cartridge has FAR longer brass life than 9mm. You can basically shoot it until the necks crack from work hardening, especially in a fully supported chamber.

Also, you can use much cheaper lead alloys for bullets in 45ACP -- again due to the lower pressure. The alloying elements used for hardening, while only a couple of percent by mass, generally account for more than half the cost of a projectile.

With 45ACP you can get away with the bare minimum tin content that you need anyway for mold fill out. With 9mm Para you are going to need to get your hands on some antimony/aresenic bearing alloy, and with the rise of lead free wheel weights that is getting annoyingly expensive.