We're a charity / school / student / good cause, will you work for nothing so that we can get a good price out of you?
So you don't believe in charity or good causes? What's such a nightmare about simply saying, "Sorry, we don't have the time at present."
I'm not really a designer but I make free pages for the local business on one of my personal/hobby site. It's amazing what a nice feeling you can get when someone tells you they got some business from that web page.