I am going next week and got an air fare out of DC for $309.00 RT. (Plus $50.00 taxes). A steal through USAIR.
You might have luck using this search engine: ITA Flight Search
It's the ITA software but now it does international flight searches. If you don't want to register just sign in as a member.
I used Travelocity and found a $364.00 flight from DC on American in early Sept. Travelocity
Try this search enigine: Quixo Airline Search Engine
Also try flying out on a Monday or Tuesday instead of a Saturday.
Hope that helps!
P.S Anybody else out there know of a good seach engine?? There used to be a search engine software that you could download but now I can no longer find it.