I've stayed at the Mariott Crystal Gateway Inn in Arlington, Va. It is a deluxe hotel BUT....here's the secret.....book it for Friday/Sat./Sunday and they offer weekend specials that can be quite affordable. It also has access to the "tube" in it's lower level so no car is needed to visit the sites of D.C. There is also an underground mall, complete with cinema down near the tube entrance. Arlington, Va. and Washington are virtually one town.
No good ideas for mid-week hotels but I believe searching the web for area "Comfort Suites" and "Best Western" hotels should give you a comfortable room with a light breakfast included.
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