Welcome to the Quilting Board!
You say "big time" contributors-where do you draw the line on the $ amount? Maybe the not so big time contributor put more time and effort in their donation-shouldn't they get something too? If they are tired of flowers-just an idea give them a gift certificate to go out to eat somewhere-I'd say everyone enjoys a night out, and you don't have to spend a lot of your time deciding what to make or how much you will be spending-I'm sure of your money.
I would put the question back on them. what did they have in mind? Large donors (several thousand $) to the local academy get a pen and ink drawing of their distinctive hall. Most people don't want dust collectors and want to know the money went to the intended purpose. For our capitol campaign we had plaques of recognition hanging in our building and a hand written thank you.
We all read..don't we? Today's post about iPads included a member posting her instructions for a 'book bench' (pillow for holding book or iPad)...I think on page 2 of posts--with pix of it. Made of velvet would surely be a unique gift for the donors. I'm making one for my reading in bed.