Fabric is not cheaper online... plus you will be paying for shipping. I'd check out all your local sources first. Quilt shops have clearance sections, and JoAnn's has 'red tag' clearance fabrics that they sell at 50% off about once a month.
Marshall's Dry Goods is the best place for selection and price, but you have to go there. They sell online, but they have too much to list on a website and it changes over pretty fast. They tend to advertise only their own lines of fabric on their website, which is not the best stuff they carry. If you are able, go to the store in person. I do that about twice a year, tho it's about 7 hours away from me.