Around $2, I think. If you're staying at a Mod or Deluxe, though, you'll have a coffee maker in your room. This is why I haven't stayed in a Value yet. I prefer the in-room coffee to the Nescafe in the food court.
You will probably save money on coffee by by buying him a refillable mug if you're staying more than 3-4 nights. But, if you'll have the dining plan, coffee can be his beverage with breakfast at no extra cost, or you can use a snack credit for coffee. Keep in mind that the mug is only useable at the resort where you are staying.