From a reader:
The notion of a lottery for Mars has been made before, and is one of several creative funding options that deserve (but won’t receive) serious consideration.
One variation that I find especially appealing is described in the book The Case for Mars by Robert Zubrin, president of the Mars Society. He proposes a series of competitions, based on a several incremental goals, each of which is a step toward ultimately getting humans to Mars. For example, Zubrin proposes a reward of $1 billion for the first company to bring a sample of Martian soil back to Earth; $2 billion for the first company to gently put a payload of 10 metric tons on the Martian surface; $3 billion for the first company to demonstrate a system that can put 50 metric tons onto a trajectory toward Mars, and so on. If I recall correctly, Zubrin actually developed that plan at the behest of Newt Gingrich, back in the 1990s.