lotusbiosm

I'm assuming you know about Craig's List (http://washingtondc.craigslist.org/). The City Paper (http://www.washingtoncitypaper.com/class/classifieds.html) also has good listings, as does The Post (http://www.washingtonpost.com/wp-dyn/content/rentals/index.html?g=1). "Cheap" in DC's going to mean something radically different than cheap in Maine. Within the District proper, some cheaper neighborhoods are Columbia Heights and Petworth. Adams Morgan's considered kind of hip, and I think you might be able to find some decent prices there. I've seen decent rates in Capitol Hill too. Georgetown, Foggy Bottom and Dupont Circle are all likely to be well out of your price range, although I'm sure you have a bit more to spend than I do. There are others too. Also, the suburbs (in Virginia and Maryland) are often cheaper than the city, but then you have a longer commute, and may need a car to go shopping and whatnot (but I think you have a car, so that might not be a problem). If you have a roommate, you can split costs, of course. I pay $615 for one room in a house, which covers rent, all utilities, cable and wireless internet (though the new tenant is paying $650 I think).
Some links:
http://www.livejournal.com/community/washingtondc/755686.html (DC neighborhoods)
http://www.livejournal.com/community/washingtondc/164623.html (Safe Places to live)