This happens quite often here at CoinQuest. People write in with an old Mexican coin and ask what it is worth. But check the date. If it looks like, for example, 1887, it is really 1987, not 1887. The strike and character formation on many modern Mexican coins are not good. It is easy to mis-read the date because the characters are poorly formed. If your coin bears the inscription ESTADOS UNIDOS MEXICANOS, which means UNITED STATES OF MEXICO, then its date must be later than 1905, when the old Mexican Republic was replaced by the United States of Mexico.
Modern Mexican coins are worth face value.