The Catechism in Questions & Answers

162. Who betrayed Jesus Christ?

One of the twelve Apostles, Judas Iscariot, visited Jesus’ enemies prior to the Passover feast. “Then [...] Judas Iscariot went to the chief priests and said, ‘What are you willing to give me if I deliver Him to you?’” (Matthew 26: 14-16).
These men offered him 30 pieces of silver. This was the amount that was generally paid for a slave. Thereby a prophecy of Prophet Zechariah was fulfilled (cf. Zechariah 11: 12-13): the Lord was, so to speak, placed on the same level as a slave (cf. Exodus 21: 32).

“Then I said to them, ‘If it is agreeable to you, give me my wages; and if not, refrain.’ So they weighed out for my wages thirty pieces of silver. And the Lord said to me, ‘Throw it to the potter’—that princely price they set on me. So I took the thirty pieces of silver and threw them into the house of the Lord for the potter.”
Zechariah 11: 12-13