Following earlier warnings about not making rash vows, God gave a way out for those who did:
Leviticus 27:13 If you want to buy back the animal [or house, or land, or person], you must pay the value set by the priest, plus 20 per cent.
It wasn’t cheap, and it wasn’t meant to be. But it gave people a chance to come back from that desperate plea of If you’ll do this one thing God, then I’ll [do something, give you something], where the something is more than the person can realistically manage.
The values were probably reasonable for their day, but the message was definitely one of don’t say it if you don’t mean it: it would cost the value plus 20 per cent to redeem (buy back) property or livestock.
Vows were serious. You couldn’t just ‘unmake’ a vow. But you could redeem the thing or person being vowed, for a price. If only Jephthah had thought more about things before making and keeping his foolish vow.