Spokes, REI and Big Wheel are the better shops that come to mind in the close in NOVA area.

Don't forget to budget for lock(s), rack, panniers/trunk bag/backpack, lights, fenders, helmet, clothing (winter, summer and rain), bell, spare tubes/pump/co2/tire levers, shoes, pedals, computer, water bottles/cages . . . . the list goes on and on. The point is, you can easily spend $500 properly equipping youself and your bike for commuting, and a lot more if your financial situation allows.