If you want to teach your child a very important lesson, you buy a 10 year old Ford Taurus with about 100k miles for about $3000. Let them drive it, them paying for maintenance, gas and insurance, for 4 years, then sell it for about $2000.
Cost of ownership - aboout $250 per year. When they start shopping for their own car, $21/month may just register in their newly educated brains as they look at new cars going leasing for $400/month.