BioShock 2 Remastered

This counts across playthroughs, reloading and the protector's trials. So if you don't have this from playing normally, reload a save when you have a lot of money, spend it all, wasting ammo if you need to. Then reload and repeat.

Or you could go to protector's trials. Killing enemies automatically gives you money, so sit next to a vending machine, and kill enemies while buying ammo.

This can easily be boosted by saving at a “Circus of Value” using all of your ammo and buying more. Load that save. Rinse and repeat