Catechism of the Catholic Church §2122 — excerpt
The minister should ask nothing for the administration of the sacraments beyond the offerings defined by the competent authority, always being careful that the needy are not deprived of the help of the sacraments because of their poverty."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.