Why didn't they ring the alarm bells earlier!? It's a bit hard to do anything now on such short notice.
I hate seeing clubs doing this, asking for donations. They should at least offer something in return, a few ideas of the top of my head:
Organise a match vs Leeds (for example). Call it the "Save Bradford match" or some other slogan so that fans know how important their presence is. I don't want to over-simplify the whole situation, but if you charge 25 pounds on the day....
25 x 20,000 = ???? you guessed it, 500,000...
or
print a cheap/crappy t-shirt that says "I saved Bradford" or something, and again, hope to sell 20,000 for 25 pounds each....
Again, you can only do so much with such short notice....