Jamieson, Fausset and Brown on Zechariah 11:12

12. I said--The prophet here represents the person of Jehovah-Messiah.

If ye think good--literally, "If it be good in your eyes." Glancing at their self-sufficient pride in not deigning to give Him that return which His great love in coming down to them from heaven merited, namely, their love and obedience. "My price"; my reward for pastoral care, both during the whole of Israel's history from the Exodus, and especially the three and a half years of Messiah's ministry. He speaks as their "servant," which He was to them in order to fulfil the Father's will (Php 2:7).

if not, forbear--They withheld that which He sought as His only reward, their love; yet He will not force them, but leave His cause with God (Is 49:4, 5). Compare the type Jacob cheated of his wages by Laban, but leaving his cause in the hands of God (Ge 31:41, 42).

So ... thirty pieces of silver--thirty shekels. They not only refused Him His due, but added insult to injury by giving for Him the price of a gored bond-servant (Ex 21:32; Mt 26:15). A freeman was rated at twice that sum.