Fred Bauder, 08/04/2013 15:38:
Don't worry. Any one who has thought about this sort of thing much has come away more puzzled than when they began. What for example is the "value" of a cigarette? The price is rather easy.
Better example: what is the value of a park, of trees in a city, of a public library, etc. Maybe the question would be "easier" to answer if rephrases as: what's the impact on HDI, on https://en.wikipedia.org/wiki/Gross_national_happiness (;-) ) or other measures that somehow numerical but not monetary.
Nemo