Donating $5/month to Kbin to keep the lights on?

I was trying to work out how much to donate to Kbin to keep the lights on. I read somewhere it costs something like $1/month per user?

Can we assume that 1/5 of users will be donating on a monthly basis?

So most people will be donating something like $5/month to cover the freeloaders and those that genuinely can't afford it?

Does that seem about right?

I was surprised to see that only 190 out of ~5k users have so far donated:
https://www.buymeacoffee.com/kbin

That maths doesn't work does it?

I hope there's a recurring payment option soon like Open Collective otherwise I'll probably forget to donate next month.