It really doesn’t do much and the cost is barely pennies per user when you operate at scale. The largest costs will be for the DNS resolver service and the domain registration, both of which you are already required to have, in order to have a functioning presence on the Internet. The cost of the issuing intermediate certificate is probably the largest single cost of the whole operation.

To be fair to Plex, they run some intermediary (caching) metadata servers to offload the demand their users put on services like the tvdb and IMDb. Honestly, is probably not required… But they do it. (I’ve seen their caching system fail more often than either site, so, it’s not all good), but even with that, you can put most of that load into your existing webhost, and it’s unlikely to make an impact on performance.

When you do this stuff at scale, the costs of simply having it set up, usually cover the costs of using it for thousands, if not tens of thousands of users.