Every Fediverse server is hosted by someone, somewhere. They can choose to handle the costs for that in any way that they wish. Some collect Patreon and paypal donations, some just eat it. Some probably plan on attempting to monetize eventually and have a roughly budgeted amount they are willing to lose first. Some will be funded and owned by Zuckerberg. Some will be run as nonprofits with a trust of some sort. Some will … etc etc. Everything under the sun basically. There is no “one way” things will work, due to the federated nature. Things will always work in many, many different ways.