Joann's sells a package of 4 -
Brand: Omnigrid
Includes four pieces per package
Dimensions: 4.5 inches; 6.5 inches; 9.5 inches; 12.5 inches;
Each has extra 0.5 inches for seam allowances and diagonal angle line
It is currently on sale for $31.49. When I bought it I was able to use a coupon - many years ago. (You can always gift away the duplicate.)
I also bought the 15 in. because I wanted to cut square of fabric for embroidery. The one I use the most is the 12.5 inch square.