At thrift stores, check in the linens section, near the sheets. Last week I found a yard of Moda fabric for $3. I use a lot of sheets in my quilting, both tops and backs. The white sheets are not see through like many quilting cottons and make excellent background fabrics. No piecing the back if the sheet is large enough. Shirts, skirts and men's pj bottoms have all been made into quilts here.