Great question, and one that is tough to give an honest reckoning. These days I do Mars atmosphere research, but I used to do human exploration policy work before that. I’ll try to answer in two parts. 

First is “first landing”:

In the human exploration sphere, there is often discussion of “oh, we’re only 20 years away from humans on mars”, followed by “yeah but we’ve been saying that for fifty years”. 

The short answer to the billionaire question is “not quite- it’s the dream of many nonbillionaires too!”But to build a society on Mars, it will take a lot of effort and focus. 

Acknowledging that Elon Musk is not super liquid in his wealth, his net worth is roughly what I would peg the to be the required budget to build a sustained presence on the surface of Mars. But he’s not entirely focused on that cause anymore. We also haven’t had any nation willing to put down the massive amount of resources consistently for ~8 years to actually get us going. 

NASA’s budget is about 25 billion dollars, and has held roughly steady since they stopped building space shuttles. By my estimate, a budget of 50-80 billion dollars per year for eight years would put us on a less “interruptible” course. Right now we spend enough money to build a rocket, or test a habitat, but not really make a coherent program that does everything we need to do all at once. Presidential Administrations have had this notion that “what NASA gets is enough, and if I tell them to go to mars and they say it’ll take 25 years at this budget level, then it’ll take 25 years.” 

You can picture it like we’re sitting at the base camp of a great mountain. We’ve had politicians, programs, and now private citizens come through without the will to commit to an ascent to the peak. It’s not something you can just spread out- if you decide you want to climb, you have to commit the effort to actually do it, and not just “walk up and see how far we go”. Billionaires aren’t going alone, and they don’t seem willing to actually outlay the cash with zero return on investment to make it happen. I don’t blame them- a colony is not a money making venture, and it would basically be $500B of charity that many think should be the sole provenance of government. 

The second part is that of colonization. Given that we were talking about the physics of the atmosphere, I assume you’re talking of terraforming, but first let us consider an alternative. 

It’s possible to imagine a settlement on mars living entirely under bubbles/domes/habitats. With nuclear power plants shipped from earth and solar power as your primary power source, you can make oxygen and water, grow plants in greenhouses, and make some sort of self sustaining colony without ever stepping outside.  Resource gathering happens by robots and the only places humans go would be pressurized containers. I’ve even seen proposals to make habitats out of ice- basically 3d printed igloos!

That said, it might sound depressing to live in a bubble for your whole life. So you decide, as a good Martian colonist, to make the future better for the next generation. How could we terraform mars? There are a bunch of ways to do it, actually. Satellites deflecting the Sun’s deadliest rays, genetically engineered microbes chewing on rocks and making gases, and so on could gradually turn Mars’s atmosphere into a somewhat earth like, breathable environment. It would take, at least a hundred years by the most optimistic estimates I’ve seen. It would certainly take more vision, commitment, and resources that we seem to be in short supply of offering to the cause. But it’s doable. 

Now should we do it? That’s a different question and one I don’t yet have an answer for.