I think that number is way too high.
The developers of Lemmy are doing it for free- unlike those of Reddit etc.
That means you just need the server resources to host the instance.
Now if you’re hosting hundreds of thousands of users, then sure it may get expensive. But the whole point is you have a few thousand here, a few thousand there, and thus the load gets greatly distributed.
Instead of 50 servers costing $1000+/mo, you have 500 servers costing $100/mo (or whatever).
And the $1000/mo server can collect enough in donations or simple ad banners to cover their costs.

What you’re missing isn’t costs, it’s profits. The little guys, and the big guys, all want to make a lot of money. They don’t want to cover their costs, they want to cover the mortgage on the beach house. Little companies often don’t make enough profit to do that, so they sell to the big guys who will slash costs and service and go profit-focused.

But start to run things with the goal of providing the service rather than the goal of making money and things change drastically. For most of its life, Reddit was ran with the goal of providing the service, which is why it grew so fast. Then a few years ago it shifted to the goal of making money and that’s when things went downhill- because they didn’t have a clue how to actually monetize the service so they pushed the ‘typical buttons’ (aka sell out the users) and of course the users are now pissed off.

But get rid of software dev costs, and look at just the hosting cost, and the number is MUCH lower.

There’s also the fact that we don’t need to host 52MM users. There aren’t going to be 52MM users on Lemmy anytime soon.