Have you considered that festivals are expensive places?
Traveling costs are only one aspect that festival visitors must consider when planning their stay. Roskilde Festival offers its own train station. Photo by Noemi Kapusy
For festivals: Consider that most NGOs don't have a lot of funding available, so think about how you can take some of the financial burden away from them. For example, allow them to camp for free, allow them to eat at crew catering, offer discounts on food stalls or allow bringing in food from outside.
For NGOs: Even if you get the festival ticket for free, you will likely need to pay for some things, if you want to realize a project at a festival. Calculate your costs for: traveling, transporting any material you need, insurances, and food. Calculate this for your whole team. Also consider what you will do in case something breaks, or other things go wrong.
Food stalls are always available at festivals, but usually they are more expensive than normal restaurants, particularly when you have to pay for three meals a day. Find out if you are allowed to eat at the crew catering for a small fee or even for free. If not, ask if you're allowed to bring your own food.