Economists figure these things out by looking at how much people value their own lives (e.g. how much of a salary increase people expect for high risk jobs). The figures calculated are surprisingly low (IIRC ~$300,000 for an Australian in the late 90s). You need to do this kind of analysis to do cost/benefit analysis -- e.g. should we spend money on making a road safer or building a new hospital?

According to Wikipedia -- $6-7M per life in the US.

http://en.wikipedia.org/wiki/Value_of_life

If you can save 1 life by spending $2.5M and instead you build 50 websites for $50k then it is reasonable to say that the site cost 1/50th of a human life.