sounds like there are two branches to this communication. I understood your question to be how much to value the quilt at for raffle purposes...I was told a few years ago that charging $15/square foot is a starting point for charging for custom quilts. That should help you in that area...you can raise the price if the fabric was extra expensive, the quilting was really detailed, etc.
I agree with the other poster who suggested that a raffle would raise more money than an auction...I donate quilts annually to raise funds for a scholarship fund and lots of people will pay ten or twenty dollars to have a chance to win the quilt, but few will offer to pay the full price for the quilt...a 48 by 48 lap/wall quilt would be worth $240 by above formula but most folks wouldn't go that high unless it's a very unique quilt, in which case, it probably would have been priced higher...