John Gill's Bible Commentary Ver. 4. And if it [be] a female , etc.] That is, of the same age, full twenty years of age, and not more than sixty: then thy estimation shall be thirty shekels ; about three pounds ten shillings of our money, the price of a servant, ( Exodus 21:32); the reason of this difference of estimation between a man and a woman is, because the woman is the weaker vessel, and her labour and service of less importance and worth, such as spinning, washing, etc.
Matthew Henry Commentary
Verses 1-13 - Zeal for the service of God disposed the Israelites, on some occasions to dedicate themselves or their children to the service of the Lord, in his house for life. Some persons who thus dedicated themselves might be employed as assistants; in general they were to be redeemed for value. It is good to be zealously affected and liberally disposed for the Lord's service; but the matter should be well weighed, and prudenc should direct as to what we do; else rash vows and hesitation in doin them will dishonour God, and trouble our own minds.
Original Hebrew ואם518 נקבה5347 הוא1931 והיה1961 ערכך6187 שׁלשׁים7970 שׁקל׃8255