I estimated it would take 40 years at $7 billion per year to create a fully closed supply chain off-Earth ("closed" = it can replicate its factories w/o anything launched from Earth.) So $280Bn. It is more than even Jeff B. has, but not too much for crowdsourcing or governments.

But that estimate may be way too high since I used comparables like the International Space Station development cost to estimate it, but industry on the Moon would be vastly cheaper, less reliable hardware.

For comparison, that cost is about 1/3 the space agency budgets of the international space station partner nations. So if they put 1/3 into starting industry beyond Earth and held the course 30-40 years, we would be there. Very affordable.