Thirty pieces of silver
Thirty pieces of silver is an expression used to denote selling off someone who is innocent for profit, or a personal betrayal for profit. It traces its origins to the Bible and Judas' betrayal of Jesus for "30 pieces of silver" (Matt 26:15). The original passage is in the Old Testament (Zec 11:12-13) and the betrayal of Jesus is considered to be the fulfillment of that prophecy.
- and asked, "What are you willing to give me if I hand him over to you?" So they counted out for him thirty silver coins. (NIV) 
- I told them, "If you think it best, give me my pay; but if not, keep it." So they paid me thirty pieces of silver. And the LORD said to me, "Throw it to the potter"-the handsome price at which they priced me! So I took the thirty pieces of silver and threw them into the house of the LORD to the potter. (NIV)