You can use the cups for soda (usually the quick service places will point you to the nearest Freestyle machine) and Icees from any places in the park that sell them, same cost for the cup. We found an 8-flavor Icee stand in the water-ride section of IoA.
We paid (I believe) about $15 for the first day of the cup and $8 for each of the next two days. So roughly $31 plus tax for 3 days of unlimited soda and Icees. Our family of 5 is OK with sharing (no germaphobes) so it was a great value for us and it kept us hydrated (and well-sugared!) We'd fill, pass it around, and refill. Since I had to put my purse in a locker for bigger rides anyways, it wasn't hard to manage.
PHXscuba