What's an inexpensive, yet good-quality & long-lasting, dark purple eyeshadow?

Try Urban Decay eyeshadows in both matte or shimmer purple! Their colors are really pigmented and amazing! If you are looking for a less expensive one try Loreal single eyeshadow shades because they literally have tons of colors to choose from. You can buy at any drugstore or Wal-Mart. Hope I helped!