Of course, fiber content, recommended care, cut, tailoring, and all that distinguishes apparel price tiers.
However, during a visit to Denim North America, one of 3 major American denim suppliers. I was pretty surprised when they showed me the identical denim that was going to Levi's, True Religion, and SFAM. (combed cotton, right-hand twill weave, synthetic indigo dye). The only difference is the design, which impacts cutting, etc, costs, and the wash, which can be pennies for groups or $20 each pair. Those washes and sandings seem to only weaken the jeans, too. High prices mean worse denim. It's beyond me.
I know whichever sewing facility constructed Wal-mart's and Victoria's Secret's unmentionables at the same quality level, too, with the same employees and machines. The only difference there is the materials (which is such a difference for me).
Usually, higher prices mean higher quality, but you have to know if what you're buying is worth it.