Numbers 18:16 (BSB)

You are to pay the redemption price for a month-old male according to your valuation: five shekels of silver, according to the sanctuary shekel, which is twenty gerahs.

From Numbers 18. Also in the ESV.

Commentary on Numbers 18:16

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Numbers 18:8-19: The priest's service is called a warfare; and who goes a warfare at his own charges? As they were well employed, so they were well provided for, and well paid. None shall serve God for nought. All believers are spiritual priests, and God has promised to take care of them; they shall dwell in the land, and verily they shall be fed, and shall not want any good thing.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Numbers 18:16: But the firstling of a cow, or the firstling of a sheep, or the firstling of a goat, thou shalt not redeem,.... That is, shalt not take the redemption price for them, but the creatures themselves; which they, the priests, were to take for their own use: they are holy; separated to the Lord, and therefore not to be used in common by men, but...
• Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Numbers 18:8-20: THE PRIESTS' PORTION. (Num 18:8-20) the Lord spake unto Aaron, Behold, I also have given thee the charge of my heave offerings--A recapitulation is made in this passage of certain perquisites specially appropriated to the maintenance of the priests. They were parts of the votive and freewill offerings, including both meat and bread, wine and oil, and the first-fruits, which formed a large and valuable item.
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on Numbers 18:8-18: Num 18:8-18 The Revenues of the Priests. - These are summed up in Num 18:8 in these words, “I give thee the keeping of My heave-offerings in all holy gifts for a portion, as an eternal statute.” The notion of משׁמרת, keeping, as in Exo 12:6; Exo 16:23, Exo 16:32, is defined in the second parallel clause as משׁחה, a portion (see at Lev 7:35).