Some noteworthy quotes from that proceedings summary:
http://science.nasa.gov/media/medialibrary/2012/01/23/NAC_Science_Meeting_ReportOctober_31-November_1_2011-finalTAGGED.pdf
It's on page 8
If quoting from the NASA website is a faux pas here, please swiftly delete this and let me know what the guidelines are. Thanks!
"Regarding costs, Dr. Karcz said that SpaceX estimates a cost of $150 million to $190 million for a launch vehicle and lander. The Dragon already has most of the necessary capabilities: sufficient lifetime and resources for a Mars transfer trajectory; atmospheric entry systems capable of guided lifting and highly capable retro-propulsion thruster. Falcon Heavy, he noted, could throw Dragon to Mars. He also noted that Dragon offers a large interior volume. He believed the EDL technology was scalable to large cargo and human landers. Assuming launch by Falcon Heavy, he said, the trunk would separate nears Mars; the capsule would decelerate through retro-propulsive action. The version under discussion would land on its legs."
"Lemke said that retro-propulsion would start at supersonic speeds. This approach, he stated, should make it possible to land the capsule at much higher Martian elevations than could be done if a parachute was used...He noted that retro-propulsion had been studied by NASA for human landings."
"the group was very comfortable that it could put down more than a ton of payload on the selected landing site."
"Karcz said the angle of attack in landing would not be controllable; however, the length of the flight path could be altered by rolling and banking. Extending the ‘flight path’ of descent would in effect, compensate for adjustments in speed."
