Bechorot 49: Maneh Tzori Pays for the Firstborn's Redemption

A new Mishna teaches us about payments that are required according to Torah law.  Different coins are required for different payments.  We learn that many payments are made in maneh Tzori, silver Tyrian coin or holy shekel:

• the five sela of a firstborn 
• the thirty shekels of a slave
• the fifty shekels paid by a rapist
• the fifty shekels paid by a seducer 
• the hundred shekels paid by the defamer 

We learn that there were two main types of coins in the time of the Torah.  Matbe'ah Tzori was considered to be biblical money.  It was a silver-based coin.  Kesef Medina had names that were the same as matbe'ah Tzori, but matbe'ah Tzori were more valuable as they were made from metals eight times more valuable than the other coins.  

It was necessary to specify which coins were meant to be used in different situations.  The Gemara notes that all payments mentioned in our Mishna consider the case of the firstborn from the other cases because they are referring to the value of a holy shekel.  Another opinion is stated by the Meleket Shalom who says that the Misha separates the case because it wants to keep separate the case of a mitzvah from cases of payment for violent or anti-social acts.  He quotes the Ritva who teaches that there is a distinction: the payment of five shekalim for redemption of the firstborn keeps its original value regardless of how currency might fluctuate.