The ancient Celts measured the worth of a human life in terms of cattle. If you killed someone, the family would demand from you the precise number of cattle associated with that person's social rank. The ancient Germanic tribes had a similar concept, the weregild, which was the quantity of gold associated with the dead person's social rank.
Nowadays, I think largely due to Christian and then Enlightenment influence, we tend to think of a human life as priceless - but do we really mean that? If, in order to save one human life, we had to bankrupt every person, every business, and every nation on the planet, would that be the right choice? If not, then where do you draw the line? Would the value of a person's life be variable based on certain factors, and, if so, what would those factors be?