I carry Hobbs 100% Wool batting and Hobbs 80/20 blend batting in 96" rolls. Cost for both is 20 cents a linear inch or (sorry for the math) .003 x square inches. I recommend the wool for large quilts since it is lighter in weight.
I usually stock various large backings, around 108" x 108". Cost is usually about $45. Below are photos of current stock. I also have a white on white floral, which didn't photograph well.