

Most of these costs are in terms of energy, one of the most plentiful things in space. Also, if we do things right (a huge if, I know), the bigger idea is to bootstrap it by sending enough tools to make the tools you need to extract and refine resources. This doesn’t require a von Neumann machine since we can control them, either directly or remotely. Also, if we are going to extract resources in space, a lot of infrastructure will need to be built first, which is cheaper if we use resources that are already in space. And as the saying goes, the surface of the moon is halfway to anywhere in the solar system.
If you compare the total mining efforts of the entirety of human civilization, it will about to a small enough fraction of the moon that it would do less to destabilize the orbit of the moon than energy loss due to tidal forces.