We also have more specific figures available because Elon Musk revealed the marginal cost of launching a reused Falcon 9 in a May 2020 interview for Aviation Week (starting at 17:53). Marginal costs represent only the costs resulting from relaunching the Falcon 9 after its first mission is already done and paid for. According to Elon Musk, the marginal cost for a reused Falcon 9 launch is only about $15 million. He explained that the majority of this amount was represented by the $10 million it costs to manufacture a new upper stage. It is not reusable (and never will be), so it is necessary to make a new one for each launch. The remaining $5 million include costs of reusing the payload fairings (Musk probably only counts fairing refurbishment costs in this scenario because it costs $5–6 million to manufacture a new set of fairings), helium, fuel and oxygen, and also the cost of recovering the booster and fairings. Most importantly, the cost of refurbishing the recovered booster is only $250,000, according to Musk. That's a very low amount, which could indicate that the booster refurbishment process does not require much manpower, expensive hardware replacements or complex inspections.
https://www.elonx.net/how-much-does-it-cost-to-launch-a-reused-falcon-9-elon-musk-explains-why-reusability-is-worth-it/
How much PROFIT did SpaceX just make?
Quite a bit.
How many more billionaires want to do this?
Over 2,000 billionaires, not to mention thousands more who are nearly billionaires. You only need to be worth about $200/$300 million to be able to afford this.
As far as I can see, the only limitation right now is that the Space Station can only accommodate up to 7 people right now. And most of those slots are taken by governments and big corporations
Of course Musk could build his own Space Station soon. I wouldn't put it past him.
It seems this is going to be a very profitable ongoing venture.