Not necessarily in Duncanville, but McKinney has The Quilt Asylum and Lewisville has Quilt Country (lots of wonderful batiks.) If I were going back to Dallas, I'd visit the fabric district just off Harry Hines Blvd near Golden D'Or. It may not the best neighborhood, but I went there alone all the time. At least one of those shops had quilting fabric at $5 per yard and many others carry garment fabrics at bargain basement prices. And Golden D'Or has amazing fabrics as well, but I think it's mostly garment and upholstery fabrics.