When sourcing onyx bathtubs, the price is primarily driven by material rarity, block integrity, and translucency. High-quality onyx should be carved from a single natural stone block to ensure structural integrity; bathtubs made from bonded stone fragments are significantly cheaper but prone to leaking. Buyers should check for natural veining patterns and ensure the stone has been properly sealed with industrial-grade water repellents to prevent staining and water absorption. Expect prices to vary based on whether the stone is Green Onyx, White Onyx, or Honey Onyx, with rare colors commanding a premium.