-Rent was under $500 - you can still get these prices. Sublet a room in a house with some other young people. - Electricity/internet bill - $35. - Cell phone - $50. - Bring down your bicycle and bike for transport - Free - If you cook every day, and eat mostly vegetarian and rice - not just MSG-infused ramen - you can live on $5 a day - that's $150 for the month. - Give yourself $250 for very infrequent meals out, beers, or BART/Caltrain trips - and surprises.
I'm guessing most of the people who said you can't do it for $1000 never tried. If you have to, you make it work.
Summer's a great time to live in SF for cheap - lots of free outdoor activities. 2 months isn't that long to tough it out. Come back again and enjoy the great city when you hit it big :)