When I took Intro to Economics, we had an interesting lecture on this subject. I'm not sure how much I agree with it, but the professor offered an equation useful in calculating, or at least approximating the value of a human life.

Quite simple, really: just multiply the amount of money per person we're willing to spend to prevent a certain risk to a life by the odds against that risk happening to any one particular person. If people are willing to spend that much, then a life is at least that valuable. If not, it is less. Rather cold, but useful to those who can easily stomach such.

Current figures estimate that value at roughly $10,000,000, depending on the social awareness of the risk and the tendency to fear it for potentially irrational reasons.

See also How precious can human life be? There are six billion people on the planet!