"While there is some room for error in interpreting Oberg's comments as to the exact cost of a Mars mission, it should be quite clear to anyone willing to look that he believes a cost below 100 billion is reasonable."

I think that a manned program to Mars could be done for less than 100 billion, I think that Larry would think this is possible.
It depends on how it is done. It also depends on how what you count the money as a cost in the program. It also depends on the nature of this program: One one way manned trip to Mars could be very inexpensive. Whereas maintaining a presence of 50 people on the martian surface for decades could be expensive. I believe that a Mars Direct Manned type mission could be done by NASA for 100 billion. I also think ISS could have been done for about 20 billion. "Could" doesn't mean "would". Nor does "could" imply a favorable probability. Bluntly, if the scope of a Manned Mars is 20 years and the budget is 5 billion per year you have 100 billion. If most of the ISS and Shuttle budget is cut by 2010, the amount savings from these programs could give you this 5 billion per year for Manned Mars mission from 2010 through 2030. Now this is may be reasonable in general terms, but it's not addressing whether it is actually realistic or doable or anything specific. Now, if you add the NASA program the development and operational cost of a Saturn V booster [or larger], this could take a huge part of that 100 billion (thereby making the total cost of 100 billion of Manned Mars, less reasonable:). If NASA wants direct control of a large booster, then a Shuttle C type booster makes some sense- NASA can simply continue Shuttle program and phase out the orbitor. It's possible that without the orbitor the Shuttle C program could have a lower yearly cost than the current Shuttle program. But that isn't saying much because the current Shuttle costs are pretty high compared to other commerical launch vehicles. Which leads one to the question why is the NASA in the launch business. The US miltary space program is lifting more payload per year and has twice the budget and it doesn't need to run a launch business. Etc, etc.

Now, the point I was making is it is impossible at this point to say what the Bush plan will cost- because the plan doesn't have enough details [yet*] and because you have to include a timeframe in the question, and/or talk about specific program. You could make meaningless predictions- such as Bush is talking about 25 years of time and NASA budget has and will increase [simply due to inflation] and he mentioned that NASA is going to Mars by around 2030, so say, 20 billion per year average times 25 years gives 500 billion. So, you could say that the Mars program that Bush talked about will cost at least 500 billion [NASA = Manned Mars plus 25 years of time = 1/2 trillion]. Or you're free to say anything stupid that you want to.

After the commission has looked at this perhaps Oberg will be able to give some kind of assessment of the cost estimate:
"WASHINGTON - The man chosen to lead the way to the moon and Mars is a one-time astronaut trainee and former Defense Department hotshot who is almost giddy about outer space travel. It's going to be fun," Pete Aldridge said in an interview. "My goodness, the president says this is what we're going to do."
...
"The commission will offer advice on Bush's plan but will not pitch alternative ideas, Aldridge said — like skipping the moon and heading straight to Mars.

"The purpose of going to the moon is a step to go to Mars," he said, and the commission won't challenge that concept. "We're not going in and saying, 'Well, Mr. President, we believe you're wrong.'"

Bush asked Aldridge to report back to him within four months of the commission's first meeting. "
http://story.news.yahoo.com/news?tmpl=story2&u=/ap/20040120/ap_on_sc/bush_s_moonman