try Ryan Air http://www.ryanair.com/site/EN/ though you may end up flying to Frankfurt Hahn or HNH as it says - which is about 1.5 hrs from Frankfurt - what a con!! - kind of like advertising stansted as London Stansted - dont get on a train in germany - i had a train ride from cologne to Mannheim and it was more expensive than the flight. - nice train though! There is a bus connection if you fly to frankfurt Hahn which will take you to frankfurt - which is an awesome city!!! Good luck dude - lets hear what you get done.

If you get your flight early enough it may be well cheap with one of the cheepy air deals.