In some cases, it doesn't even last that long... Maybe in the case of a special ammunition that can aid the massive destruction of a special character/adversary in some rounds, you may be requested upon to buy more on arrival...
Overwhelmed with the bouts and adventures in the game, you may not even realize how much you've spent until when you've decided to quit for the day.

I don't think it does hit as hard as casino games (especially since I'm not expecting something very fungible) but this time, as long as money leaves your pockets, it's definitely what it is -- gambling!