Isn't Kagi mostly just a meta search engine aggregating results from the usual suspects with some added independent index building?

That's not exactly a rare feature, in fact most independent search engines do exactly that (querying the big searches while building their own index on top), and for free.

Also you can self-host a metasearch engine (for example: see here) or use one of the several dozen ones other people self-host and make available to the public.