It's ridiculous what stuff costs-- regardless of whether it has to do with airports, rest stops or other places. That's a LOT of money for a bottle of water... but as the saying goes "they have you by the short hairs."
Many years back-- when I was living in Austin, Texas-- they built a new airport. And conducted a brave new experiment-- NO chains, only local providers AND nobody could charge more than the price in their local store or eatery. Don't know if they still do it... but it was a pretty revolutionary idea.
All this makes me want to dust off and finish my partially written piece on the human "greed gene!"
The only Airport that I have ever been in that has "real world" prices is Milan Malpensa. It's interesting to read about Austin but I will be even more interested to read your finished article on the human "greed gene"!