Backs and batting are my largest expenses as I try to use stash. Unfortunately I have fewer and fewer pieces of yardage at 6+ yards. I'm getting pretty creative over piecing backings -- more and more by choice, but there is an ease and joy in the extra width that I also appreciate and maybe even prefer if usually out of my price point...
I know eQuilter has offers on shipping and international orders, especially if you can order multiple pieces and total over $100 which is, as you are finding, just a couple of backs and that also usually gives you a coupon for your next order. They have options starting around $14 yard US/regular price for the extra wide.
https://www.equilter.com/
Many times at Joann the extra wide backs are not on sale with the rest of the quilting cottons and you can use those half price coupons!