I would think the value of all your materials and a "reasonable fee" for the sewing/quilting of the quilt.
They may need it for several reasons... they might wish to give you a receipt so you can deduct it on taxes or they might need to have a value to advertise what the prize is worth or again, they might need the value to give to the winner of the auction (something about the difference in the price they pay and the value of the item being tax deductible).
If in doubt, ask them why they need the value and go from there.