Yeah, you're not really paying for the soda. You're paying for the labor that goes into providing the service, maintaining the equipment, etc. Oh, and the paper cup which probably cost more than the liquid you put in it. The high margin on things like soda also subsidizes the cost on lower margin food items.

The true value of soda is also somewhat obfuscated by the fact that most people's point of comparison is packaged soda. A bottle you buy at the store also didn't necessarily cost a lot to make, but actually distributing pre-made soda to retailers is a lot more expensive than shipping syrup which can be mixed with water on-site. That added cost is built into the price of packaged soda.