The best place to start looking for a sail is from this website. They have quality sails at reasonable prices. When you purchase a sail you need to consider the parts that go into the sail. The weight of the cloth has little meaning to the quality of the end product.
Be sure that when you do your comparison shopping that you specify the same hardware, the same sail cloth make/mfg, the same dimensions, reef points, stitching etc. Without all of the same components you are not comparing apples to apples.