What is the average economic value of a human life?
It depends on the context, of course, but most often in policy analysis "the value of a life" has nothing (directly) to do with output, etc, but instead means the maximum amount that people would want the government to spend in order to save a randomly chosen life.  

So in a country of 300,000,000, the question is:  What, to you, is the monetary equivalent of a 1/300,000,000 chance of death?  Because 1/300,000,000 is a very small number, we don't have to worry terribly much about willingness-to-pay versus willingness-to-accept.  (Theory tells us that for small changes, the two willingnesses are effectively equal.)

Returning to the question:  How much would you be willing to pay to avoid a 1/300,000,000 chance of death?  Now multiply that value by 300,000,000.  That's the value of one life, and arguably the amount we'd want our government to spend to preserve a randomly chosen life.  

Obviously there are problems with heterogeneity (you and I might not answer the question identically).  But as a general rough rule, the estimates tend to come in somewhere under $10 million.