Joanne's always has some coupon on their website. Sometimes it's a percentage off one item, which sounds like it will work for you when you want to order your batting. I'm not sure if the single-item ones are good on sale items, because I don't use these and haven't paid that much attention to them. The one I see there now is for 30% off a regular priced item (some exclusions apply, like irons and sewing machines).
Sometimes the coupon is for a percentage off the whole order, including sale items. These are the ones I use, since it's not worth it for me to drive out there for one item, and it's not worth it to order one item online and pay for shipping. I think I've seen 10%, 15%, 20%, and 30%, but the 30% is rare. I've gotten some fabric for less than $3 a yard. Not nearly as nice as the LQS fabric, but it helped me build a small stash without spending thousands. Now that I'm not stash-building, I don't buy at Joanne's much.