Re: Hello from Virginia (NOVA)!
You have a couple options here. Baltimore, Annapolis, Deale, Solomons all have a lot to offer and not a far drive from Metro DC but none are cheap, they are crowded areas and you are paying Maryland taxes on your boat. Again not cheap.
The Virginia side of the Potomac is quite rural, very un-crowded and as I mentioned, the lower Potomac is a very big river. You can find a slip in Westmoreland or Northumberland county for quite a bit less than the areas I mentioned above and taxes, especially in Northumberland Co. are VERY reasonable.
What kind/size boat are you interested in getting?