How often?
Well if we launched 100Klb 4 times per year, and that was say 30% supplies and 70% module, then after the same 5 years that we've been building ISS, then we'd have a 56-tonne space station (that's 4 747's) with ~18 habitable modules, 20 crew and a dozen dumb return capsules.
Plus the supplies to keep it going all that time, and engines and fuel to keep up the reboosts.
All for the same cost of Shuttle+ISS.
What it takes is some simpler thinking and less frivolous innovation. - big ugly dumb modules. Perhaps a framework of second stage tanks as volatile storage/structural framework/options to install doors and make them further modules.