It despends A LOT on where you live. Just look at barns around your area and remember to compare not only costs but also the barn itself
I charge 45$ for a group lesson, which is up to 5 people.
At mine a private 1 hour lesson is $40 but if you do a group lesson for 1 hour it's $30 per person
At the barn I ride at group lessons of 2 or 3 people last 1 hour and cost $60