If you are young (20-30), single, and are willing to have roommates to group up into some apartment, then SV may be an adventure for you. However, as you grow in life, you will need a pretty high level of income to feel secure in this environment.
Start-ups would be better off setting up shop in underdeveloped parts of the country, however, as the cost of labour here puts a serious overhead over any fledgling company.