I’d pay to avoid having to use Facebook. Not sure how much, though. Maybe up to $500 a month if it became mandatory under some authoritarian regime but you could opt out via a fee.
To force me to use Facebook? It’d be a lot. Maybe $10,000 a month, if I were to use it every day and as most people use it, with relatively honest information. I am not sure $10,000 a month would be enough. Maybe more. I’d definitely use it if someone paid me $50,000 a month. So somewhere between $10K and $50K a month would be my required Facebook usage payment.