Many hikers make weight and compressibility the primary consideration in choosing a bag, but you should recognize that a comfortable sleep is worth hauling a few extra ounces up the trail. Price, budget Dream of the perfect bag if you want, but limit your search to what you can afford. We all started with equipment that was barely adequate and we had a great time anyway. You won't get something for nothing. When considering cost consider also longevity and quality of the product.
Reliability also costs more.
Cheaper products may have to be replaced more often and won't magically keep you warm. Learn the principles first then know your compromises when you make your decision. In most cases, there will be a bag in your price range that can fit your needs. There are many different shell fabrics available for sleeping bags. As water resistance increases, breathability often decreases.