Bayview is has cheaper real estate than the rest of the city because it's considered one of the most dangerous places in the city to live.
Here are some Yelp-like reviews of the neighborhood: http://www.streetadvisor.com/bayview-san-francisco-san-francisco-county-california
Bayview is still very much an area-in-transition, but it's close proximity to some of the last remaining public housing projects left in SF and it's much cheaper cost of living sets it apart from the rest of the city. If you lived in Bayview, you'd most likely draw your culture from the SoMa area about 5 minutes by car to the north. SoMa is young, techie, and fairly vibrant, located very near to the downtown district.
Hope this helps!