Since you'll be commuting south, I would recommend something in the southern districts of the City. (assuming you're limiting yourself to SF proper, not other communities on the Peninsula)

The Mission comes immediately to mind. Close to the freeways, great public transport, alterno-hipster + vibrant immigrant scene. Since you're willing to share a place, you should be able to find something in that price range.

Potrero Hill, SOMA, Noe Valley, Glen Park could be other alternatives.

Let us know more about what you're looking.