We have set up a Patreon account for anyone who wants to contribute to the operating costs of the ohai.social server: https://www.patreon.com/ohaisocial
It is entirely optional to donate. We understand that not everyone is in a financial situation to spend money on a social media service and we want ohai.social to be a welcoming place for everyone, regardless of financial status. 
That said, if you are able to chip in a few bucks, we very much appreciate it.
We currently estimate the operating costs of the server to be around €350 per month. I know that's a bit vague, but it's difficult to gauge costs this early on since we use a cloud provider with variable billing and it's tricky to project how many people will join in the coming days.
But just to be clear, there is no chance of ohai.social going offline even if we have zero patrons. Any donations just help reduce the amount we have to pay out of our own pockets 
ohai.social team
Julianna Thompson