I have provided coffee to my maids before. But they bought it from the supermarket very often like every 2 weeks - 3 in 1. then they told me three maids each drink 3 coffee per day. So we limit to one cup per day only.
Everything if I give them they will just ask for more. You give coffee then later they may ask for soft drinks or juice.
So better not to be so relax at the beginning. Once you have provided, you cut back then they will feel you are very mean!
I provide coffee for my maid. I buy from Parkn shop during sale, usually $39 per box (42 packs). And she also buy some by herself from indonesian shop. I know she drinks 2 cups of coffee each day.