Good luck! Be sure to establish a beginning price that covers the cost of cloth, thread, % of machine upkeep, etc. I don't put in my time because I don't know how to price that. When I do even simple quilts, lap robes, I find that my materials cost $60 to $70. That is my base price range.
Having said that, consider using double sided adhesive batting. You can make bigger blocks or strips or ....? and piece them together and adhere them to the sandwich right away when you get the width of the quilt done; then start on the second row. The back can be a single piece. When you get going with this method you can make a quilt in a day (I always have trouble with the binding, but still can get it done in a day). My daughter tells me that lap quilts and bed runners are the best to do because they are more versatile and more people will bid on it.
Either way, put a bottom line price and if it doesn't sell they can give it back to you. It is too demeaning to have a quilt you've worked on and like enough to put out there and have it sell for $20 or $50! There is no reason for you to work hard and essentially give your work away. I was scared to do this the first time, but my husband insisted I bottom price it, at the very least, to cover the cost of the materials. The group putting on the sale decided to jump the quilts I offered (there were four) up to $100 each and they all sold. Not much $ for my labour, but the cause was a good one and we all were happy!