Airline pricing is often complex, but there are two general factors that influence the affordability of airfare: the demand for a flight and the supply of flights. Sometimes, it could be more affordable to book connecting flights on more competitive routes as opposed to a direct flight on a less competitive route.  For example, it may cost $400 to book a flight from London to Chicago and only $300 to book a flight from London to Milwaukee with a layover in Chicago. A traveler looking for savings would book the latter and leave the airport once his plane lands in Chicago.