I suspect others do this as well, but I always buy a 3 to 3 1/4 yard length of fabric for my borders. That is done in the planning stages, unless I have made my blocks out os scraps. I fold it 4 times as suggested, (along the selvege adges) and cut off the selvege on the one edge I am cutting the borders from. I usually apply the side (vertical) boders first, since they are the longest. Then I apply the "head and foot" borders last. If you want to use the same fabric for binding (and I do) you still have that length of fabric to cut in strips ( if you want to make a straight binding) or you can cut the fabric on the bias for a bias binding (which I prefer.) It sounds like a lot of fabric, but if you cut it early in the process, you can use the left-over in making blocks for your quilt, so it does not appear to be a "foreign" addition to your quilt.
We are all happy to share what works for us. Keep asking.
June in Cincinnati