[mikoto]

http://www.variac.com/staco_Variable...former_Map.htm
http://www.action-electronics.com/variac.htm
A VERY little info plus links to a few products: http://www.elect-spec.com/variac_tutorial.htm

I think this sort of thing is the most elegant solution. There are cheaper ways but I'm not the expert so I'll not put foot in mouth.