You could try and make a DIY swamp cooler? There’s lots of instructions online for how to make them, and basically the only consumable is water. The only caveat is that they work by drawing hot air in from an open window to evaporate water, so it’s not very effective in high humidity or low temperatures.
I think posters/flyers are one of the most powerful ways to reach people in a local area, you’ve got to be in the local area to see them, right?
Another way to spread the word can be via the internet, Facebook is god awful, but a lot of communities will have something akin to a noticeboard that is another effective way to get the word out.