256bits said:
Do you know anyone with that amount of cash lying around?
Elon Musk.
Putting aside the economic considerations, one should solve the engineering and technical issues, which must be addressed before putting a cost on it.
Before landing someone(s) on Mars, it would be prudent to send a craft to land on Mars, and more importantly, lift off Mars to orbit, and then return to earth. Then we can begin to define a manned mission. And perhaps before that, send a crew to Martian orbit, and then bring them home to earth.
How long would such a mission last? One year or perhaps more likely two years or more. Note, the orbital period of Mars about the sun is 687 days, while Earth's orbit is 365 days.
Mars oppositions happen about every 26 months. Every 15 or 17 years, opposition occurs within a few weeks of Mars' perihelion (the point in its orbit when it is closest to the sun).
https://mars.nasa.gov/all-about-mars/night-sky/opposition/
https://mars.nasa.gov/all-about-mars/night-sky/solar-conjunction/
https://en.wikipedia.org/wiki/Orbit_of_Mars
Next opposition - Mars will reach opposition – when Earth will pass between Mars and the sun – on December 8, 2022.
Planetary Society - Humans Orbiting Mars, before Humans on Mars.
https://hom.planetary.org/
In 2014, the National Academies released a report which concluded that NASA's current plans for getting humans to Mars could not happen earlier than 2046 without a massive (and unlikely) increase to the human spaceflight program's budget.
In response, The Planetary Society held a workshop in the Spring of 2015 to explore a proof-of-concept plan which could get humans near Mars over a decade sooner. This is known as orbit-first.
Instead of landing on the first go, NASA could lay out a series of missions that use existing programs, strategically build experience and capability, and spread out cost. The orbit-first concept would send astronauts near the Moon throughout the 2020s, to Mars orbit and Phobos in 2033, and finally to the surface of Mars by 2039 to begin an ongoing program of exploration.
https://www.nationalacademies.org/n...eded-in-space-nuclear-propulsion-technologies
https://www.ida.org/-/media/feature...-a-human-mission-to-mars-by-2033/d-10510.ashx
https://www.nap.edu/read/12409/chapter/26
https://ntrs.nasa.gov/api/citations/19710011960/downloads/19710011960.pdf
There needs to be infrastructure 1) around earth, the departure point, 2) transit system to and from Mars, 3) around Mars, the arrival point, and 4) surface of Mars for those landing and remaining for some time or permanently.
ISS could be such a facility, assuming it is still viable for the next 10 to 20 years. There needs to be some orbiting station around Mars (with food, water, oxygen). Related to infrastructure item 2) is a periodic supply system (unmanned). Most likely, supplies for a manned mission would be sent in advance of 2), 3) and 4).
There have been lots of studies on missions to Mars, including putting a manned base on (actually in) Phobos, which is close to Mars (nominal (mean) distance from Mars, 9377 km).
https://mars.nasa.gov/all-about-mars/moons/summary/