If you get on mailing lists, the companies will let you know about sales and free shipping times. Save up your purchases and get free shipping. I find the prices at Hancocks of Paducah are wonderful with a huge selection and even better when on sale. Their Kona Cotton is about $5.50 all the time. This company was highly recommended by another blogger who uses them often:
https://www.whittlesfabrics.com/ The Fabric Shack in Ohio is a good internet company.
These are just three. Again, sign up for email and you will get notification of sales and other specials.