How much should I save up to move out of my parents house with 2 room mates?

I am moving out of my parents house at the end of this year, and I am trying to save up as much money as possible. I'm 19 years old, and live with my very over-protective parents. I am a full time receptionist for a government agency making $12/hr for the time being. I plan on moving out with my 2 friends at the end of this year- into an apartment that is $680 a month with water and sewage already included. I don't have car payments- I inherited a car from my aunt. My cell phone bill is roughly $50 a month, and my gas usually adds up to about $140 a month. I can bring my bed and any furniture that I already have, so I really don't have much that I have to buy. How much should I save up between now and December? Thanks!