What about this ...
The official Arduino team checks out this project to see if it is kosher.
If it is the Arduino folks set up a system where we can contribute money to a fund to pay for the Arduinos.
When the Arduino folks have enough money they can send the Arduino Unos to the project.
This won't cost the Arduino folks anything except some of their time - and maybe they would be kind enough to make the Unos available at cost price.
If they do set up a fund like that I would be prepared to contribute the price of one Uno - as long as I can pay with Paypal to an Arduino account. I am not prepared to pay anything directly to the charity.
...R