Traffic in the DC area is a challenge. A lot depends on where specifically you will be working, and the nature of your boat.
The bridges over the Occoquan are pretty low for most sailboats so that is not an option for most people. If you have a boat that will fit under the Rt 1 and railroad bridges PM me for a reference to a marina there.
Sailing on the Potomac is poor.
Herrington Harbour North takes liveaboards and has a lot to offer.
There are a number of good choices in Annapolis. Ask for details and I will elaborate.
If you are truly downtown and can manage the waiting list, Gangplank Marina or Capital Yacht Club are good choices. Things are a little gritty on the waterfront but there is a lot to be said for public transportation in DC.
You should expect about 7 or 8k / year for a 40' boat.
There are lots of places South of Annapolis you could moor or anchor out for less. There are private docks as well, but you need to be local to find them.
sail fast, dave