It is worth it to get the wide backing, and there is so much more choice now than there used to be. But one other option, if you want a particular fabric, is to use the diagonal cut method. Just buy a little extra in length, cut in half diagonally and slide one side down until the width is right. This way, the seam is evenly distributed the length of the quilt. Here is a calculator:
http://www.multi-patch.com/html/diag...calculator.php