On a schoolhorse? Here it's minimum $36 (group) up to $70+++ depending if you want a level 3 or Olympian level coach (Leslie Reid). That's a cost anywhere from 30mins-1hr. The $36 is for a 45 min lesson that frequently runs longer haha.

I currently pay $50/lesson on my own horse with a great coach and that includes her travel fee to my facility because I don't board at hers, which would be $40/lesson if so.