Because granite is an extremely common mineral on earth, most of that 2-inch granite ball's cost was the labor-cost of shaping it and polishing it to "glassy" shinyness. As you know, the price of Collectibles varies a lot, depending on the selling location. At a fleamarket, your shiny 2-inch granite ball would sell for about $5. In a Mineral-Collector shop, probably around $10.