If you are going to use public transport your commutes will be very, very long to any DC area airports, even assuming there is a bus line as was mentioned for GAI, so it may be worth it to buy a $1500 commute car. Years back I lived in NW DC as well as Pentagon City in Arlington, VA and instructed out of Potomac Airfield (VKX) ... which is now the closest rental/instruction airport to downtown DC by far, but one of the 'DC-3' airports that require pilots and renters to gt a special background check/security clearance thingie and get a discrete squawk code and talk to ATC for every flight. It is still operating and is just 30 minutes tops in good traffic, but then, DC rush hours with the commute flow can be nasty and run from 3 pm to 7 or 7.30 pm. In any case, VKX is too far from any bus line.
Reverse commuting is often a piece of cake though unless you have to get on the beltway (no real reverse commute on that parking lot). If you're going to use Metro, aim for a commute that will avoid a line change. Are you in DC proper or in VA or MD, and N, S, E or W of the downtown core? That all makes a huge difference. If you lived near an airport, you could use a bike or Vespa or something on most all flyable days- not fun though for heading home in summer thunderstorms and winter sleet. All in all living in Montgomery Co. and using GAI is probably your best bet for being carless. E of DC, Bowie airport is literally right off of route 50 so perhaps there is a bus line that stops nearby, you can try calling the airport. Way up north, I'll bet FDK Frederick, where AOPA's HDQ is located, is probably near a bus line. Call AOPA and ask.
