Good luck with this sizable fixed funding campaign.
My concern is that no matter the quality of compelling story you capture the festival programmers may have a tough sell with a ticket paying audience.
What you might consider is making the "cultural phenomena" not quite so on-the-nose and in-your-face!
First, I wouldn't legitimately consider "outsider" support of anything to be all that strong.
I'm not going to donate to all sorts of stuff that doesn't have a darn thing to do with me, and I don't think that's a very unique perspective at all.
So, the support and interest SHOULD come from the community affected. (This is a problem I have professionally and with the U.S. military and financial "contributions" to many global local communities: If the individual/community doesn't give a sh!t I have a difficult time giving a sh!t on their dumb lazt @ss' behalf. F#ckit. If they don't care I don't.)
Then what you could/should do is determine WHAT the relevant community DOES shell out cash for, provide a heaping pile of THAT, hopefully "outsiders" will ALSO be interested in that same commodity, then serve a subversive side story B along with that primary interest.
WHAT does your research indicate Native Americans DO pay money to go see?
WHAT is their primary form of visual entertainment?
You gotta figure out what they DO care about.
Give then THAT with a side order of "B."
HOPEFULLY, more than just their community will ALSO be interested in the same main course.
Yeah, apparently from what I was told, they don't want help from outsiders and I was like wow....they said the fight is "theirs" so...I said whatever....anyway I spent all last night putting together a new film project, so I'm set to move on......