Abigail Breslin got top billing for "Zombieland" on the movie's IMDB page -- but that doesn't mean she's pulling in top dollar.

The 13-year-old's contract -- which is on file with the L.A. County Superior Court -- shows she was paid $100,000 for the flick ... not exactly Cameron Diaz money.

But don't cry for her too much ... Abigail will get bonuses starting at $50,000, depending on how much the movie pulls in.

Here's the deal -- even if the movie bombs, $100,000 is way more than you made at 13 ... and us too.