London-area public transport puzzle

As a purely theoretical exercise (ahem), how does one get from Stansted Airport (friday morning) to some place near Tottenham Hale (and back on sunday afternoon/evening), as fast as possible, without using the horribly expensive Stansted Express.
To get you started: http://www.travelinesoutheast.org.uk/ , http://www.arrivabus.co.uk/ .