John Tierney, strangely enough, has a good idea:

Instead of just financing NASA's plans for Mars, Congress and the White House should make it compete against engineers like [Burt] Rutan. It could offer a prize, to be awarded by the National Academy of Engineering or the National Research Council, for the best plan on paper for a manned mission to Mars.

I don't think we should decrease NASA's funding, and I certainly don't think we should force it into any sort of "earn-your-dinner" competition for appropriations; on the contrary, I think it's a shame we don't spend more money on NASA. But without getting into that debate, surely it wouldn't be too hard to shift around a couple of non-NASA budget line-items and come up with $10 or $20 million (which, for reference, is about one-eighth of the cost of a new F/A-22) to give some private-industry types the incentive to get involved in the space program. The X-Prize proved that you didn't need to spend a gazillion dollars to get people excited; the winning team (led by the above-mentioned Rutan) spent about $25 million to win the $10 million award. So let's put some money out there, give people some time, and see what happens. It can't hurt.