Matthew 17:27

στατῆρα (ἵστημι, ‘to weigh’), ‘a stater’; a Greek silver coin equivalent to the Hebrew shekel, or to four drachmæ in Greek money, hence sometimes called τετράδραχμος. ‘In paying the temple-tax it is necessary that every one should have half a shekel to pay for himself. Therefore when he comes to the changer he is obliged to allow him some gain which is called κόλλυβος (see ch. Matthew 21:12). And when two pay one shekel between them each of them is obliged to allow the same gain or fee.’ The collection of the Temple tax was made in Adar, the month preceding the Passover. Lightfoot, Hor. Hebr., Matthew 21:12.

ἀντὶ ἐμοῦ καὶ σοῦ. Cp. Exodus 30:12-16, ‘The rich shall not give more, and the poor shall not give less than half a shekel, when they, give an offering unto the Lord to make an atonement for your souls’ (Matthew 17:15). It is in accordance with this thought of atonement or substitution that the preposition ἀντὶ is used.