I find that funny, it is a common myth that motorcycles are cheaper than cars.
I'm glad you are amused but my 35 years of riding experience tells me it's not a common myth. In many cases (though not all of course) a motorcycle can be much cheaper than a car to purchase, maintain and even insure.
Part of the argument that cars are cheaper is based on servicing them, which many car owners simply don't do.
It depends on what you are comparing.
Compare any car to this.
Kawasaki Ninja 250 (fully capable of freeway speeds, of carrying hard bags and extended rides and touring)
Initial cost: $3,000
First Service: $250.00 (if at dealer)
Gas mileage: 65+ (yes, 65+ mpg)
Insurance (rider over 25): 180.00 year.
Chain at 15,000 miles: $150 (if replaced at dealer)
Rear Tire at 15,000 miles (they last that long on this bike): 150.00 if replaced at dealer.
Even if the engine only lasts 50,000 miles (which you can get out of the little thing if you take care of it), that's still only two of these in 10 years for a total cost of $6,000 purchase price.
You can buy 5-6 Ninja 250 motorcycles for the cost of an entry level honda or Toyota.
It really depends. The most expensive production BMW isn't more expensive than many entry level cars. Most Japanese motorcycles are less expensive than almost any production car to purchase. Most production motorcycles get 40mpg.
So they can be cheaper.