Trying to Find My Sister.

Hi every one im very new to Forums..and well im trying to find my Sister who my mother had to give up due to hard times..this is about all i know she is two years younger then me so that means she was born 1991 i think in july and she was born in GA in Clayton County At Clayton General Hospital and she was adopted out to sandy springs city .. from what i could get out of my mom it was an Open Adoption. my name is Patricia and our others name is Sandra...i dont know if since it was an open adoption if that means i can just call up for free or if they would charge me and arm and a leg..