An internal NASA study found the fuel depot option to be $79 billion cheaper ($64 billion versus $143 billion) than a Space Launch System option and the fuel depot option would be 5 years faster for Near earth Asteroid mission.
NASA had actually been rather busy studying those very topics. The conclusions that NASA arrived at during these studies are in direct contrast to what the agency had been telling Congress, the media, and anyone else who would listen.
This presentation "Propellant Depot Requirements Study - Status Report - HAT Technical Interchange Meeting - July 21, 2011" (69 pages) is a distilled version of a study buried deep inside of NASA. The study compared and contrasted an SLS/SEP architecture with one based on propellant depots for human lunar and asteroid missions. Not only was the fuel depot mission architecture shown to be less expensive, fitting within expected budgets, it also gets humans beyond low Earth orbit a decade before the SLS architecture could.