Well the cheaper places to stay would be in the burbs of DC or Baltimore. Both areas have lots of public transportation so that will be helpful. You are going to be coming around the tail end of the Cherry Blossom Festival in DC..
http://nationalcherryblossomfestival.org/cms/index.php?id=390 So you may want to try to catch some of that. It also means DC will be CROWDED..The festival is one of the big events here. The Nats home opener MIGHT be difficult to get into, usually the bigwigs snatch up all the tickets for opening day and if Obama throws out the first pitch..well...
Lots of good places to eat. Just about any type of ethnic food. If you want good crabcake I would recommend Phillips Seafood in either DC or Baltimore (there's a nice one in Baltimore's inner Harbor).
Thats just a few things off the top of my head. Be glad to answer any specifics you have.:)