Hi Mel,
Welcome from NYC! There are no Walmarts in or around the city. The nearest would be NJ or Westbury LI. However, the one in Westbury has a miserable fabric dept. (at least last time I was there they did)Can't speak for any others. There is a Joann's in Westbury also and they have a good selection. Right in Manhattan is The City Quilter. A gorgeous shop, but, being a quilt shop - prices are high. But you really should stop in and see it, even if you don't buy. Maryupnorth mentioned the fashion district, but finding 100% cotton quilting fabric isn't that easy. However, you can try. The City Quilter is in the fashion district, so you might enjoy a visit there and strolling around and checking out the other places. Truthfully, I think your best bet if you're looking for good prices would be your idea of ordering online and shipping to your friend's cousin.