1) By a quick look online plane tickets start at about $120 one way.
2) No idea
3) On the cheap for hotels food? How cheap do you want to go? Days Inn or Motel 6 is about the cheapest you will find. Rates will vary wildly between different parts of the country with NYC and LA probably being the most expensive. In many areas you can get a sparse but clean room for $30-$40 a night, you can probably tripple that for NYC. Insane. Cheap food? Fast food resturants or even better, mom and pop resturants.
4) Long time, California is HUGE.
5) No clue
6) Probably Budget, but someone else would know better.
7) For regular unleaded about bteween $1.75 and $2.20 depending on where you are. Figure in a compact rental you will get about 25 miles per gallon.

Yeah stay away from everywhere you mentioned. I'm sure I will piss some people off for saying this(sorry), but why visit the places you mentioned? NYC and LA are the left and right armpits of the US. Atlanta? That's the rectum of the US.
There are so many places to see in the US, the big cities is the last place I'd recomend. Big cities suck, period. But then again it all depends on what your interests are. Personally I'd say instead of Atlanta, go airboat riding in the FL everglades. Instead of LA, go see the Grand Canyon. Instead of NYC go ANYWHERE :lol: