Hi there!
I love nonprofits who are doing great things! The only thing I love more than nonprofits are nonprofits in education! In fact, I am working on building a business right now where 50% of the profits go to improve literacy throughout the world :)
But, enough of me blabbing. You're probably much more interested in talking about your project. Haha, I have read through your project description and I would love to help you in this goal.
I am bidding below your budget, because I'd like to help your non-profit succeed as best as possible and I think others are overbidding. You see, from what I understand, the site your looking to have would best be built with wordpress. It does not make sense to me that others would charge you more to code from scratch and take longer. Wordpress is the ideal CMS for your site, because you can easily select a template of the site you like; I can set it up, add the donation button and email list; and have it ready insanely quickly. It is also ideal because wordpress is the most commonly used CMS out there (I bet 1/2 the sites on that link you listed use it), so there are tons of developers for it. Also, most wordpress themes are already responsive so your site will be perfectly ready.
I would really love to talk more with you about your site and how I can help you in this project, but I'm limited in the amount of words I can write, so please message be by clicking the button below my name so we can discuss the site :)
Thanks,
Jacob