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.
       Gold Marble
Gray Leaves
Dark Blue Leaves
Dk. Muslin Floral
Lt. Brown Floral
Off White/Black Floral
Tanner loves his quilt!