It depends where you're going to be in Northern VA. Most of the stores around the beltway are way overpriced. I would look at one of the following stores:
Quantico Tactical - Woodbridge, VA
VA Arms - Manassas, VA
Bullseye Guns, Leesburg, VA
These 3 stores price almost everything pretty fairly in my opinion. I would call ahead to make sure they have them in stock.