I would recommend visiting and getting a short term accommodation near Roma Norte. There's a few peripheral areas around there that haven't had as much price inflation, but you'll want to identify them by physically being there as there's other closeby areas that you don't want to be in (Doctores).

If you're willing to go a bit further south in the city (45-60 minutes from Condesa, depending on traffic), Coyoacan is a great area. I haven't lived around UNAM but I hear it's very lively. You could also go for a more tranquil existence even further south in Tlalpan, or go east outside the city to a colonial style town like Valle de Bravo (known for its lake and paragliding). A lot of your preference will depend on your level of Spanish and how much you like being around expats.