Leviticus 27:8 in the World English Bible
But if he is poorer than your valuation, then he shall be set before the priest, and the priest shall assign a value to him. The priest shall assign a value according to his ability to pay.
Context
7 And if it be from sixty years old and above; if it be a male, then thy estimation shall be fifteen shekels, and for the female ten shekels.
8 But if he be poorer than thy estimation, then he shall present himself before the priest, and the priest shall value him; according to his ability that vowed shall the priest value him.
9 And if it be a beast, whereof men bring an offering unto the LORD, all that any man giveth of such unto the LORD shall be holy.