You aren't going to get a self-sustaining colony on Mars for the cost of the Apollo program. Just getting a biosphere-level of sustainment would be several ord

You aren't going to get a self-sustaining colony on Mars for the cost of the Apollo program. Just getting a biosphere-level of sustainment would be several orders of magnitude more expensive. If "self-sustaining" is meant to mean an insurance policy, then it requires more than just generating food and water; it will require a whole manufacturing base. I don't think 10+ trillion dollars, about three orders of magnitude more than NASA's budget either now or during Apollo, is unrealistic at all. For comparison, the space station cost $150 billion 2010 dollars (according to Wikipedia). It is in low-earth orbit and satisfies no conditions of self-sustainability. With a factor of 100 on that, which is impossibly optimistic, you are already at $15 trillion.