How about this... Mars: Tax Haven.
All the billionaires will move there for the tax dodge.
If the billionaire converts their wealth into dollar bills and carries them on their spacecraft to Mars, about their only use would be to burn them for warmth when they get there.
Money left in bank accounts on Earth will be subject to the taxes of the jurisdiction of that bank.
Those billionaires will also need to pay large "fees" to support the infrastructure that keeps them alive and supplied. Though not truly taxes, they might as well be.
Hard to imagine such practical types as these rich folk wanting to leave it all for the colony. NSoV, as usual.
The speculation of $500K one way tickets could work, I imagine, if there is two way traffic. Ya go, ya stay for a couple of years, ya come back. But the larger issue of growing an economy strikes me as interesting.
So. You preposition two years of supplies for the first four or six one way candidates, promising them that you'll be back. Up there it would be a barter economy geared to survival only. Every two years another four, six, eight, dozen or so people would show up. I could see a yearly launch rate of low energy robotic supply missions which would start making the long term survivability of the colonly more and more feasible with each successful landing.
Eventually, that one billionaire who wants to get away from it all shows up, since survival rates would have been demonstrated. What will he pay some of the other colonists to wait on him hand and foot? How would that economy grow from a bartering of services and common ownership of real property and infrastructure? At what point can there be differentiation of labor, where garden duties can be traded for mining duties, or rover repair duties? Since there will be some labor specialization already, like the rover repair guy and the gardener gal, how would the labor exchange rate be determined? At what point do they start xeroxing money and IOU's?