What's the basic price range for across the country road trip?

I'm going into 9th grade, and I make money from my grandma and get it from Christmas and my birthday, summer 2015 ( when I graduate ) me and my 2 friends are planning on going on a road trip, we're ALL going to save up all four years. I'm making goals and my goal for the end of year 9th grade is $1,200. I was just wondering, how much money (All of us together) are going to need? (we live in Michigan, we plan to goto New york, Chicago, Los Angeles (big cities)