AMD High Performance 1 vCPU, 1024 MB RAM, 25 GB NVMe, 2.00 TB Transfer
Emails are sent using zoho mail free tier. If absolutely necessary an additional $2 for two users (admin and noreply) /month would be added.
Total cost (yearly): $96 + (some tax).
As things stand right now ~$100/year is easily affordable but as the number of users grow, it largely boils down to egress and storage costs. I can personally bear most of it, but if it starts booming then I'll have to rethink about options.
Currently we don't have anything setup (we're just too tiny right now). I'm talking to other instance admins about best practices around donations/tips.
I'm looking into Open Collective as the platform to accept donations at some point.