Sounds cheap. All of Earth's space countries could pay a billion or two a year and pay it easily. At least initially while it grows.
Economically speaking Mars would not achieve economies of scale needed for becoming self sustaining.
Manufacturing every component for higher safety standards than commercial aircraft or nuclear submarine is expensive. Building whole society that works in safety critical environment 24/7, starting from daycare and ending with microprocessor and chemical plants is just fantasy in the near future.
Maybe in 100 or 150 years we can start dreaming.