Well, lets break it down like this:- fuel is at least $3.40 per gallon and fuel burn is a minimum of 5 gallons per hour so one hour's flying burns off $17bucks per hour. It doesn't take long to work out that 20 bucks an hour is impossible! The aircraft has to be purchased, maintained and then there is the overheads and profit! I think that if you are teaching a guy to drive who claims to have a pilots licence, then maybe he is in the land of the fairies!
The realistic rate is around $100 per hour for the aircraft rental and then there is around 30 bucks an hour for the instructor if needed!