Leviticus 27:8-10

Amplified Bible

⁸ But if the person is too poor to pay your valuation, then he shall be placed before the priest, and the priest shall value him; according to the ability of the one who vowed, the priest shall value him.

⁹ ‘Now if it is an animal of the kind which men can present as an offering to the Lord, any such that one gives to the Lord shall be holy. ¹⁰ He shall not replace it or exchange it, a good for a bad, or a bad for a good; but if he does exchange an animal for an animal, then both the original offering and its substitute shall be holy.