Honestly you can go very far with unmettered data plans. We consume 2GB/S, maxed out, which ends up being 5184TB a month. We have millions on users a day, all on a streaming video platform. It cost less than $2K/Month. The cloud is crazy expensive. Private servers are beasts, and they are cheap. Of course, for this price, you don't have redundancy and horizontal scaling. You also don't have to maintain and debug a sy…
Not including extra human cost in the analysis is just disingenuous. I think to manage private servers of that size you would need at least two extra experts totalling at least $20k/month.
What? You set up the deployment once, and then you only need to touch it when things go horribly wrong, which is every couple of months, or to make minor quick tweaks and run some updates. Let's be generous, and say you need 10 h/month, which is about 1/16 of a person-month. And if things go horribly wrong, everybody drops what they are doing to fix things, anyway, no matter if you're on AWS, dedicated/colo or run your own data center.
When you significantly change your architecture/deployment, then you need to put in more time again, but if you build your code with need to scale and such things in mind from the get-go, then that won't come up much or at all.