It's a great idea and it doesn't take long to strike a balance. The people you want to work with will soon get an idea of how much time/money you are willing or able to expend; the ones who want to take advantage, or don't understand just how much time and effort you are putting in, will soon fade away. It will take a few weeks/months to sort this fully.
I generally contribute film and proofs, and where appropriate, final prints too, all at my own expense -- though (for example) the Tibetan Government in Exile has also paid internal air-fares in India, plus accommodation and food.
As well as the Government in Exile, I have also worked (in various epochs) for inter alia a cyclists' action group and our local parish church (Anglican) in the UK and la Hermosa Ciudad de Guadalupe in California -- which was fun because Padre Julio was Panamanian Catholic, the police chief was American Mormon, and I'm a Cornish Buddhist...
Yes. Do it.