The United States has a human space-flight program that bypasses the lunar surface in favor of missions to near-Earth objects and Mars. These are laudable goals, but the moon also has much to offer. Limited budgets probably preclude a U.S. government-sponsored human lunar exploration in the coming decade; however, the possibility exists for such to be accomplished by private enterprise. It is posited that, to bring costs within a range that might make a business case close, the mission must be relatively austere and make maximum use of existing assets and capabilities. This paper reports on a study conducted to evaluate the feasibility of lunar mission architectures primarily using as much existing or in-development, commercially available hardware and technology as possible. In particular, dual Earth-orbit rendezvous-lunar-orbit rendezvous and dual launch-lunar-orbit rendezvous missions are studied using existing and in-development flight systems as examples. The solutions described here are found to be feasible, to substantially reduce development requirements relative to recent post-Apollo approaches involving entirely new launchers and crew capsules, and to offer the possibility of human lunar expeditions at costs not unlike robotic flagship exploration missions.