It is possible to get from Manhattan to the three major airports in NYC (JFK and LaGuardia) and New Jersey (Newark) via public transportation for under $10. However, it would involve multiple train and bus changes and about 2 hours of commute time. A quicker way to the airports would be to use the yellow cab/taxi but it will cost anywhere from $35 to $50.
Two other cities are participating in the mid-month subway theme: