Leviticus 27:13

But if he will at all redeem it
The owner of it, or he that has devoted it, if he is determined to have it again at any rate:

then he shall add a fifth [part] thereof unto thy estimation;
he shall give the full price for it, as rated by the priest, and for which it might be sold to another man, and a fifth part of the value of it besides; this was done that the full price might be paid for it, the priest not knowing, as it might be, the worth of it so well as the owner; and that the value of consecrated things might be kept to, and to make men careful how and what they devoted, since, though redeemable, they were obliged to pay a large price for them.