196 - Helium3 may indeed be worth going to the moon.
If, we ever figure out how to make a fusion reactor. (We have been trying for 50 years and haven't figured it out yet). But perhaps someday we will.
So, at $10,000 per pound, how about give me a general WAG, at the cost to build a helium3 factory on the moon, and a transport system to bring the helium3 safely back to earth.
You need not include the costs to invent and build fusion reactors on earth, for this question.
Feel free to round off to the nearest Trillion$.
That may be just one of the products that is useful, however, the gravity well is what makes the Moon so attractive.
Have to run dang it, will post more tonight.