I researched this last summer after a head-scratching convo at work with three well-versed long-time DMVers. No one was really sure of the answer. I used a regular handle (1.75L) of Smirnoff vodka, which is a fine standard vodka, for my comparison test.
This handle is always $21.90 (45 shots=49¢/shot!), and sometimes even on sale a few times a year for $18.95, at the VA ABC.
In DC I went to Congressional Liquors on Capitol Hill. No handles for sale, but they did have a fifth (750 mL) for $14.95. Wow, what a mark-up!
On to MD. At the time I was living in Huntington so I crossed the Woodrow Wilson and went to Seitz Liquors in Oxon Hill. A handle of Smirnoff there? $26.50! They tossed in the uneasy feeling with all the bullet-proof glass in the place for free.
Now maybe you've got the scoop on a great deal somewhere in DC/MD, but VA has their prices licked from what I can tell. And going into a VA ABC is quite the pleasant experience as opposed to the train-wreck liquor stores I've seen in multiple other states, including Maryland.
If you'd like to check it out, VA ABC publishes a quarterly price-list of EVERY offering in PDF form:
http://www.abc.virginia.gov/Pricelist/price.html