It depends on where you are for the specific languages, but there is a general expectation of value for goods and services. In that hypothetical the customer could just refuse to pay the egregious amount and leave, the establishment could sue, and a court would end up figuring out the fair price in arbitration or trial.

Granted, the hypothetical is ridiculous, but it's good to apply the systems we have to the ridiculous so we know they can handle real situations, which tend to be so ridiculous we can't even make them up.

You expect certain prices based on experience at other establishments. If a particular bar or café has prices that are egregious vs other comparable local places, it probably won't stay in business long. So I'm never that surprised when I get the bill, even if I didn't scope out the prices first. And if the price is shocking, that's on me for not checking first. Lesson learned and I won't go back to that establishment.