Exegesis:

echarēsan ‘they were delighted.’ Subject is the chief priests and the captains.

sunethento autō argurion dounai ‘they agreed with him to pay (him) money.’

suntithemai ‘to agree,’ ‘to covenant,’ ‘to promise.’

Translation:

They were glad, or, “greatly pleased” (New English Bible), or, ‘they rejoiced’ (for which see on 1.14).

They … engaged to give him money, preferably, ‘they came to an agreement with him to give him money.’ Judas’ part of the agreement has been indicated in v. 4; the part of the chief priests and their associates is indicated by this last clause of v. 5; hence one may have to render it, ‘they came to an agreement with him, saying (or, promising) that they would give him money, or, pay him for it.’ For money see on 9.3.

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.