There are some people hosting their own identity server, but yes the centralisation of the main aggregator server seems to be by design as they even scare people away from trying by talking about the high resource requirements of doing so.
IMHO Bluesky is only federated in the sense that responsibility for content and moderation can be outsourced, but the user endpoint stays mostly in control of Bluesky. This makes a lot of sense if you think about it from a company perspective… outsource the legally and personnel critical parts and keep the ones that are lucrarive for advertisement and can be easily scaled by throwing hardware at it.
But you must be a real sucker to take them up on that very one sided offer…
Lemmy.world used to cost that much, but I think they downscaled a bit recently, or are at least planning to as the current growth of the userbase has slowed down.
I was actually surprised by that 150 figure when I first read it, as it is much cheaper than what the BlueSky documentation makes it sound.
It is certainly possible to collect that much in monthly donations, but then again… how do you build a loyal base of supporters for running a mostly hidden piece of infrastructure? People always complain about the instance focussed nature of the fediverse, but the ability to build communities around them and get people actually emotionally invested in their home instance is IMHO rather a strength of it. That is also why I am slightly sceptic of easy account migration tools, as it devalues the instance as yourhome base to a certain extend.