How much will it cost to have people live on Mars?

Answer 1

There aren't yet any good estimates of how much it will cost to send people to Mars, or to keep a Martian colony going long enough for it to be come self-sufficient. It will be literally "astronomical".

Whatever the cost, it will be cheap insurance for the human race, which could be exterminated with a single asteroid strike on Earth. Once humans can survive on Mars, and the Moon, then one catastrophic accident won't inevitably mean the death of the human race.