What is the cheapest way to travel from Dortmund, Germany to London, England for the weekend?

I need to travel from Dortmund to London multiple weekends this summer to see my girlfriend, leaving friday afternoon and returning by monday morning. Flying Easyjet would run around $180, travel by train would seem to take 6-9 hours each way even with a Euro rail pass, and car rentals would be in the $200 range, after gas. Help?What is the cheapest way to travel from Dortmund, Germany to London, England for the weekend?Cheapest way would probably be to fly:

http://www.easyjet.com/en/book/index.asp

If you book in advance you will pay approx. EUR 100,- for a return flight to London (Luton).