I suspect he (and we) would be far better off chucking this money at nuclear fusion research.
I think this is the correct stance.
There are three major existential threats to the existence of humans on Earth, all of which are good reasons to become multiplanetary: global thermonuclear war, runaway climate change, 10 km asteroid. (Supervolcano might also be on the list, but it's hard to say.)
The second could be partly if not completely neutralized by fusion energy and carbon capture. The others can only be survived by establishing a self-sustaining and
reproducing and growing extraplanetary colony.
Fusion energy would likely have remarkable benefits beyond the existential threat, however. At this point the applicable terrestrial infrastructure gains from manned space travel are low, though the scientific gains remain high. The scientific
and infrastructure gains from fusion energy would be world-changing.
Nearly unlimited free energy would
also remove one of the major problems of building a self-sustaining extraplanetary colony. If we dump a fusion reactor and robotic construction apparatus on the surface of Mars
first, getting humans to survive there is now 100% easier.
Fusion research, meanwhile, isn't getting funded at nearly the levels it needs to be. We have already achieved breakeven. There is
no reason why we shouldn't be spending trillions on scaling this up
right now.
Oh right, we have to spend those trillions on standing armies.
The real existential threat to humanity? Humans.