Just a quick note. The B30 express bus from BWI doesn't go to the Blue Line; it goes to Greenbelt, the north end of the Green Line. You can still transfer to the Orange Line at L'Enfant Plaza. Or you can transfer at Gallery Place to the Red, go one stop to Metro Center and then catch the Orange Line.

Additionally, coming in on Thursday or Friday, you can catch a MARC (Maryland Commuter Train) at the BWI Amtrak station (free shuttle on the lower level of the airport to the train station) to Union Station (then catch the Red Line on the Metro to Metro Center and the Orange Line transfer). Returning home on Sunday will require an Amtrak ticket (or take the Metro method back to Greenbelt and catch the B30 north). Returning on Monday will allow you to catch the MARC train back to BWI. MARC trains cost $6.00 one way from BWI to Union Station, DC.

Being in Maryland, I'm not familiar with the VRE (Virginia Commuter rail) routes and schedules, so I don't know if they are an option from Reston.