Kommentar zu Wajikra 27:4

ואם נקבה הוא, “and if she (the subject of the valuation) is a female person;” ולנקבה שלשים שקלים, “and the valuation of a female during the same age group is thirty shekel.” Basically, the monetary value of a female person is roughly half of that of a male. This reflects the fact that the first woman, Eve, had been taken from the body of the first man, so that G-d’s work was only half that of what it had been when He created Adam, the first human being.