You are correct, all the money in the world is insufficient. Which is why we need resources from other worlds/asteroids. People aren't going to leave earth unless they can make a buck or gain fame. As with royalty of old, we need government to fund exploration for future commercial development.
I do not think it is a false dichotomy to say that we must expand or collapse. Certainly the Earth is not completely exploited but we will eventually tap out the easy resources. Is that the time to begin to act or now when we have resources to spare?