Complementary coins

hi there
In a bar setup i would like to give out complentary coins. 1 coin equals 1 non alcoholic beverage.
Does anyone have a suggestion on how to implement something like that?
important is that the item obviously has to be deducted from the inventory but also that i can see the total cost-price of the complementary items.
i hope i have been clear enough with my explanation.

all tips/tricks/suggestions are welcome…

Default gift option would do that, make item free, remove from stock and show total gift value :person_shrugging: