Leviticus 27:8-10

New Catholic Bible

⁸ But if anyone is too poor to pay the estimated value, then he will present himself before the priest and the priest will make an estimation based on the ability of the person vowing to pay. The priest will establish the value.

⁹ “If he brings an animal as an offering to the Lord, then everything that he has given to the Lord will be holy. ¹⁰ He should not exchange it, a good one for a bad one or a bad one for a good one. If he should substitute one animal for another, then both the original and the substitution become holy.