What is the cheapest public transportation to go from intersection of K St and N Capitol St Nw to IAD airport

What is the cheapest public transportation to go from intersection of K St and N Capitol St Nw to IAD airport?
I am gonna take megabus from buffalo to washington, dc and gonna get off at the intersection of the K St and N capitol St NW around 1 am. I have a flight to catch from the Dulles airport (IAD) at 6 am. What are the options available for the transportation?
Other - United States - 2 Answers
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1 :
There's no public transportation that will be able to take you to the airport at that time in the morning. The earliest bus to Dulles from DC leaves at 5AM, too late to make your 6AM flight. I suggest that you take a cab. NOLA Guy: He's arriving at 1AM... the MetroBus to the airport doesn't run at that time.
2 :
You can take MetroBus: http://dc.about.com/od/transportation/a/DullesAirport.htm http://dc.about.com/od/transportation/a/Metrobus.htm