Family based immigrant visa, can I petition for my parents without an Affidavit of Support?

My name is Stacy and I am a U.S Citizen currently a student at RPI in Troy, NY. My parents are both Mexican and live in Mexico. In March I turn 21, and I would like to file a petition for my parents. It is my understanding that one of the requirements to file the petition is for me to sign an Affidavit of Support. I would like to know if there is a way for me to claim my parents without being required to state that I can support them financially, because I can't. My parents can support themselves financially on their own. Please let me know if you are able to help me, and the fees you charge for my case. Thank you,