First of all, I think the fediverse, the good one in the future, is made of lots lots and lots of small instances.
Why?
Because FB, Reddit etc "brought" all the forums, homemade sites etc that existed before together in one place, regrouped them by helping everybody, and then when having the control, enshittifying it all to monetize it...
So for me, in the long run, sites should probably be about one thing, not like "everything".
That said, most small specialized sites could probably run well on a shoestring budget or almost for free (I put up an old PC with a lemmy instance and except the time it's just the electric bill I'll pay when I don't need heating, for example).
So should you give money to the "big" sites? Really, I don't know, probably today yes to have the "Lemmyspace" running. To a small community if needed, yeah!
I think it's a complex question without a good simple answer.