Do you have any intentions of breaking down the costs and sharing them? I'd be curious to see as to where some of that could be going. Especially in relation to travel costs/any gear rental. As others have said: they've got some experience in this sort of thing. The input at least might help with cost reduction.
70k for a documentary does seem like a steep cost. Especially when feature films with entire film crews and gear can be made in a month for 150k. Ideally a documentary would have 3 - 5 behind the camera: sound, lighting, DP and 2nd AC.
For a documentary I can't see a whole lot of money being needed for the gear side of things, given you just need a few lights and some materials. Camera doesn't need to be an ARRI Alexa or anything too fancy either, even a Sony A7 3 would suffice. Ideally a group hired directly from a production company that does documentaries would also have access to such gear already. The fee would more be for hiring them for their work over the gear.