There is no set price for lessons - they can vary greatly from one
instructor to another. The price difference can be attributed to a few factors: the length of the lesson (this can range from 45 minutes to 2 hours), the experience of the instructor, the size of the class and natural market factors like supply and demand. The following are a few price examples:

Toronto, Canada:
Group classes average CND$10 to $15 per hour (US$7-US$10)
Private classes average CND$40 to $60 per hour (US$28-US$40)

New York, US:
Group classes average US$15-20 per hour
Private classes can range from US$50-$120 per hour

Group classes are usually once a week, and can vary from 5 to 10 lessons. Group classes are a better deal if you pay up-front for the series of lessons, i.e. 6 lessons at $10 would be $60 versus paying 6 lessons at $15/drop-in class which would cost you $90 for the same number of lessons.