One word: competition. Only if they have a legal monopoly (e.g. patent) can someone charge what the market will bear. Once that expires, the market will be open and competitors will appear based on how excessive the first company's mark-up is. Once the mark-up drops to a reasonable profit level, no new competitors will come in. Then you have stable pricing. Like in laptops and desktops today, for example.
As to your beverage example, I'm pretty sure soda companies advertise. Yet a recent article said that 70% of marketing costs are spent to ensure shelf space. So there are plenty of other costs besides the bottle, flavors, sugar and things like RO filtering etc.