If a company has a monopoly on ALL soda (Coke, Sprite, 7-UP, etc) and prices go up too high, people substitute with drinking milk or juice.
A hypothetical for the sake of discussion: What if the same soda company also had a monopoly on the dairy farms, orchards and even the distilleries?
I would open one up in my backyard, massively overhype it, and when they come to buy it up sell it to them for 100x what it's actually worth. Rinse and repeat until they're bankrupt.