How much server costs for an SaS application?

Edit: Damn spelling mistake in the heading … SaaS.

We are currently at the concept stage for an SaaS plattform. Unfortunately, we don't have any experience on how much a server cost (for larger applications). Maybe there is somebody who can tell us some numbers? Nothing in detail just for a rough calculation.

Our needs: – 20 – 50 GB per user / month – 3.000 users – node.js backend – MariaDB – traffic according to GB per user

I know, that's not much details but I'd be very grateful!