What is the meaning of Matthew 26:15?

And said [unto them], What will ye give me, and I will deliver him unto you? And they covenanted with him for thirty pieces of silver. (Matthew 26:15 KJV)

and said, What are ye willing to give me, and I will deliver him unto you? And they weighed unto him thirty pieces of silver. (Matthew 26:15 ASV)

and said, What are ye willing to give me, and *I* will deliver him up to you? And they appointed to him thirty pieces of silver. (Matthew 26:15 DBY)

and said, “What are you willing to give me, that I should deliver him to you?” They weighed out for him thirty pieces of silver. (Matthew 26:15 WEB)

‘What are ye willing to give me, and I will deliver him up to you?’ and they weighed out to him thirty silverlings, (Matthew 26:15 YLT)

Interlinear

And said <epo> unto them, What <tis> will ye <thelo> give <didomi> me, <moi> and <kago> I will deliver <paradidomi> him <autos> unto you <humin>? And <de> they covenanted <histemi> with him <autos> for thirty <triakonta> pieces of silver. <argurion> (Matthew 26:15 KJV)

Albert Barnes’ Commentary

Verse 15.  And they covenanted with him. Made a bargain with him. Agreed to give him. Mark says they promised to give him money. They did not pay it to him then, lest he should deceive them. When the deed was done, and before he was made sensible of its guilt, they paid him. See Mt 27:3; Ac 1:18.  

Thirty pieces of silver. Mark and Luke do not mention the sum. They say that they promised him money–in the original, silver. In Matthew, in the original, it is thirty silvers, or silverlings. This was the price of a slave. See Ex 21:32. And it is not unlikely that this sum was fixed on by them to show their contempt of Jesus, and that they regarded him as of little value. There is no doubt, also, that they understood that such was the anxiety of Judas to obtain money, that he would betray his Lord for any sum. The money usually denoted by pieces of silver, when the precise sum is not mentioned, is a shekel –a silver Jewish coin, amounting to about fifty cents, [or 2s. 3d.] The whole sum, therefore, for which Judas committed this crime, was fifteen dollars, [or 3l 7s. 6d.]  

{x} “covenanted” Zec 11:12,13; Mt 27:3