How about 2USD/year? WhatsApp ran on 1 until Facebook bought it.

I did the math at the time: with the users per server and separate user stats they were publishing, each employee could be paid very, very generously. Don't quote me on it but I think it was something like half or a quarter million per year. Yes, they were small and growing, as you grow you get more overhead as you try new things like eg. business customers or whatever, so maybe it can't be 1/year anymore (also because a decade of inflation happened in the meantime), but you can get very close to that or choose to operate in low and middle income countries at break-even or a small loss. I wouldn't find that unfair (as someone who earns in the top 1% of worldwide incomes, household income like 150k/year -- yes I'm looking into how to put that boatload to good use -- and who would be paying the compensatory high price).