Refillable mugs are $18.99 and can be purchased and refilled at Kalepa's Store (next to the main lobby), the Lava Shack, and One Paddle, Two Paddle. They have a unique design compared to the other Disney Hotels.
Even though they seem pricey, the mugs are well worth the price just in the wonderful coffee alone. Soda at the pool is a bonus. I believe you can fill your mug (coffee) as early as 6 AM at the O'lelo room.