Is it possible to find this config in a pre-built solutions /w waranty? They do not feel comfortable with custom built systems, I like them personally, but the vice-director feels otherwise.
Give Dell or HP a call and see what they can do for you. They may be able to off a special deal because your a non-profit group. You never know till you try.
In that regards you might see if some of the majors are willing to donate some low end computers as its 100% tax write off anyways and you could offer them some sort of free advertising as in tmhe for of a link of banner on your page to thier site.