@joeld @shram86 @shine @timClicks I'm not comparing between countries though.
The billionaire is looking for Java engineers in Europe, for $80-120k of presumably contractor money (otherwise the sum would be quoted in euros), so I'm comparing it with European salaries. If an engineer in Germany would sign a non-employment contract with said billionaire for $80-120k, that would be roughly equivalent to them signing an employment contract with a local company for 65-95k€ (or 57-85k€ if the quoted amount does not include typical 5-6 weeks of vacation).
This is more on a low side in Germany, and that's not even counting that they won't be protected by labor law.
So this incredible offer sounds like a joke in EU (in Germany at least; i'd imagine in other western European countries too).
I don't know if that's an okay salary in US, or what net income would it imply in US. I don't think it's relevant, because job and seems to be for Europe.