Judas Iscariot
There are several explanations as to why Judas betrayed Jesus. In the earliest account, in the Gospel of Mark, when he goes to the chief priests to betray Jesus, he is offered money as a reward, but it is not clear that money is his motivation. In the Gospel of Matthew account, on the other hand, he asks what they will pay him for handing Jesus over. In the Gospel of Luke and the Gospel of John, the devil enters into Judas, causing him to offer to betray Jesus. The Gospel of John account has Judas complaining that money has been spent on expensive perfumes to anoint Jesus which could have been spent on the poor, but adds that he was the keeper of the apostles' purse and used to steal from it.
Bargain of Judas
The Gospel of Mark and the Gospel of Luke mention no price. The Gospel of Luke states that Satan entered Judas to prompt him for the bargain:
Now the Feast of Unleavened Bread, called the Passover, was approaching, and the chief priests and the teachers of the law were looking for some way to get rid of Jesus, for they were afraid of the people. Then Satan entered Judas, called Iscariot, one of the Twelve. And Judas went to the chief priests and the officers of the temple guard and discussed with them how he might betray Jesus. They were delighted and agreed to give him money. He consented, and watched for an opportunity to hand Jesus over to them when no crowd was present.