question

Since you're talking about a multiplayer game, the first thing to understand is, how do you plan to manage the active session?

If you're using custom game servers, part of your total cost will be the server hosting fees. How many users you can host per server is going to be largely determined by your code, so that's not something we could calculate for you, but the cost for hosting custom game servers in PlayFab is the actual EC2 cost plus 10%. You can see the cost for all EC2 instances here: https://aws.amazon.com/ec2/pricing/on-demand/, under the Windows tab. You can also host in any other game server provider you like, if you prefer. The advantage to hosting in our service is that we automatically spin up/down servers according to need, and we capture the log and output files from your servers so that you can retrieve them later (for tracking down any reported issues).

You could also use Photon Cloud, from Exit Games. Our integration with Photon Realtime provides you with simple authentication and webhook callbacks into Cloud Script handlers, though you wouldn't have full server authority in that model. Pricing for that is as shown on the Photon page in the Add-ons Marketplace, in the Game Manager. They also provide Photon Enterprise, which does provide full server authority. For that, you would need to contact the Exit Games team directly, to get info on pricing.

Finally, if your game is fully asynchronous such that you have no need for any custom game servers or Photon (players only make a few moves per minute at most, and you're able to drive the server checks you need in Cloud Script), and you don't need any upgrades (if you do, pricing for those is shown for each via the Settings->Limits tab), it's technically possible to run in our free tier. We do not limit the number of players in the free tier, but I should highlight that it also does not provide any SLA. We do everything we can to help everyone out, but we do have a responsibility to the folks with whom we have support/enterprise agreements to make sure their issues are resolved first. I would always recommend getting some form of agreement with us that provides an SLA, for any professional developer. If you'd like to discuss that with our business team, feel free to open a ticket with us on this page.