"money shall he pay": R. Yossi Haglili says: We have not heard how much. I, therefore, reason as follows: It is written here "money," and elsewhere (re one who was ravished, Devarim 22:29), "money." Just as there, fifty, so, here, fifty.
Rabbi Yosei Haglili Confronted a Problem in the Torah's Legislation
Mekhilta Tractate Nezikin 17:12