All the fundamental technology needed to mount a Mars mission within a decade is in place. I mean engines, tanks. It shouldn't take much longer than that to build a few rockets. But remember, we want more than a one shot deal. Space is cheaper than a fleet of B-2's, and a lot more useful.
Infrastructure is to be minimized.
Creating liabilities by inflating the cost of a program won't encourage anyone to provide the funds to sustain it. I've had a lot of experience talking to the general public, not just space cadets, about manned missions to Mars, and I can tell you that they support the idea enthusiastically. The problem is that there is a disconnect between the public and Washington. We need to mobilize the support that is already there. They've done that, now it is up to all of us to do the work to insure that the campaign succeeds.