An informative contribution from Robert Fitzpatrick to one of our discussions:
It depends on the city in the USA. In NYC, many teachers (especially of voice) command at least $200/hour with some studios considerably higher (perhaps approaching and exceeding $500/hour) Those who teach in a conservatory actually make a bit less per hour but their reputation inflates the rate they can command from external private students. Some are actually worth it. An hour with an inspirational master teacher is always priceless.
Contrary to what most folks assume, teachers at Curtis and Juilliard on hourly contracts usually make less at the school than their external rate. Full-time contract salaried teachers are expected to teach18 hour per week (but most do a lot more voluntarily).
Josef Hofmann’s hourly rate for teaching piano at Curtis was $100/hour in the 1920s*. Hofmann hired Auer and offered him a bit more than he made for teaching.
I know of one important NYC teacher whose rate decreases for the most talented (to the point of not charging at all).
*Equivalent to $1,300/hour today