I have a rough enough idea of how much image hosting costs. If they want to charge more than a dollar per month I will write a competitor.
0: https://drewdevault.com/2014/10/10/The-profitability-of-onli...
https://www.statista.com/statistics/251328/facebooks-average...
($53 per US user)
Now, whether asking users to pay for a social network at all is a viable business model, is another question.
If you are seriously considering paying for the poison that is Facebook, might I recommend you delete your Facebook account instead, and give your money to someone that needs it?