I want a chevy coballt but my parents want to give me the G35???

Your first car should be a SAFE car with all other considerations second. Civics and Cobalts etc DO NOT hold up in a wreck especially with a large PU or SUV 4X4 they will slide under it and kill you airbags won't do any good. Get a Ford Ranger or Chevy S10 they get good mpg and are more reliable than either of those cars. Better yet get a full size PU that way you can get work moving etc and pay for it and with gas the way it is you won't have to drive to see your folks and grow up!