I think you are too late to score AA's O-fare (their deepest discount fare class). I'm doing another MR this weekend on it--IIRC $175 fare round trip DCA-SFO via DFW; typically AA fares will work in both directions). This fare requires a Saturday night "stay" (just have to be there at midnight--my layover is less than two hours, then red-eye back

)
Go to AA.com and plug in the airports, than select search by PRICE, and it will try to come up with something for you. You will have to play around with the dates (and you can try "dates flexible" option).
You can also try
http://search.travel.yahoo.com/bin/s...intl=us&oc=bwi and plug in your airport codes, for a more general search where you can see the fare rules for the cheaper fares.
Steve