The cost of sending materials from Earth to orbit is indeed high. And we're unlikely to be getting up there whilst this is so.
The cost of sending materials from orbit to orbit, however, are significantly lower.
All we really need to lift is a seed factory, and a few "tugs"(these could be assembled by the factory, in orbit) which can then tow LEO debris to the seed factory where they can be used to (mostly) allow the seed factory to expand it's facilites until the point it can clone itself, print some more tugs and a couple of centrafugal launchers. The launcher can throw a couple of tugs out to the belt between Mars and jupiter. Then it can throw the cloned seed factory, the tugs can catch it and position it. Few weeks later it can throw a centraugal launcher, same story. The tugs can feed that factory from the belt, if it throws 70% of processed materials back this way, and keeps 30% to upgrade itself, then by the time the first materials get back to us, it's already cloned itself and there's twice the resources inbound. Then double that, then double that, then double that, then double that .... Exponential growth.
Then we can entertain crazy projects, like attempting to house our population...
By the time the first resources arrive, the Earth-side seed factory should of significantly cleared LEO debris, and constructed manufacturing and production facilities. Just the other side of the moon I'd suggest mining facilities for when we start stealing asteroids out of their problematic orbits and strip them bare. For such operations, something like a mylar bubble I don't know if it will be strong enough - but there needs to be some procedures and equipments utilised in order to ensure we don't create any more debris in the act of mining.