there is a good book on that subject by Richard Dolan called The Secret Space Program and Breakaway Civilization.
video also relevant
the answers to your question about funding sources encompass mundane things like drug trafficking and securities market manipulation, as well as more sophisticated funding mechanisms that require some preliminary study before one is ready to understand them.
I hear ya, there is a tremendous amount of nonsense out there on this topic.
I like Dolan's work because he is an academically trained historian who sticks to what he can glean from declassified govt and military documents and in interviews or 'oral histories' undertaken with govt/intel/military personnel who claim to have worked in these programs.
Dolan has done a good job of ignoring the small army of channelers, reiki practitioners, and others who sometimes get involved with this topic.
One angle that, over time, I have come to view as especially compelling is that of interstellar trade. If space exploration efforts from the 1950s onwards uncovered intelligent life visiting our neck of the woods, it's conceivable that exchange of goods or resources sprang up - and much of the off-the-books funding for covert programs in space could be coming from this untaxed trade with select spacefaring civilizations presenting barter opportunities.
At 30:15 in his new video, Giuliani emphasizes that Ukraine was a center for Dem Party corruption, not only that of Joe Biden.
Let's see how hard POTUS's lawyers go after corrupt Dems other than Trump these next few days at the peach mint.