There are many options for housing in the Bay Area.
As a USF Graduate student, you have access to USF Student Housing and Residential Education resources. Although the majority of graduate students live off-campus, you may consider living on-campus in Pedro Arrupe Hall or Loyola Village.
Two additional very helpful and free resources for housing include Craigslist and SFGATE, San Francisco Chronicle's website.
If you wonder what the cost of living is like in San Francisco, get an idea by visiting the San Francisco Chamber of Commerce or City and County of San Francisco websites.