When the price goes up, naturalization rates go down. The current filing fee for Form N-400, the Application for Naturalization, with U.S. Citizenship and Immigration Services, for adult applicants is $680 ($595 plus an $85 biometric fee).This is certainly a prohibitive cost for individuals living below the poverty level.he current filing fee for Form N-400, the Application for Naturalization, with U.S. Citizenship and Immigration Services, for adult applicants is $680 ($595 plus an $85 biometric fee).