London is always dirt cheap in the winter, this past weekend the weekend specials had it for $229, total round trip cost, all taxes included, from New York. Train to Washington and back costs more.

There is no rhyme or reason to airline fares, or else a flight from new York to London with the connection in San Francisco on both legs wouldn't cost less then round trip from new York to San Francisco.

One of the beauties is the cost isn't mileage based anymore, so there are some very good deals out there.