[Also posted in DC Forum...]
Assuming Fairfax means George Mason, you likely want to base yourself along the
Metro Orange Line. Easy access to downtown, and there are frequent shuttles back and forth between the Vienna station and the Mason campus. So you'd kind of be looking for things from Ballston on out to Vienna. Housing gets cheaper (though not by so much) the further out you go, but that comes with increased commuting time and cost. So that might be the area to start looking at...western edge of Arlington, Falls Church, Dunn Loring, Vienna, Fairfax.
There are a lot of housing options, and because of the many government people who get assigned out of the area for a few years at a time, there is usually a good stock of TH and SFH rentals out there. One place to look for rentals that many people don't think of is a site called
MilitaryByOwner.com. You don't have to be military to use it. You do have to pick a nearby base -- Fort Myer will do fine. Even if you don't find the perfect place there, it's typically useful in getting a feel for what's actually around...