Kind of a cool little animation of how Injection Molding works.
The whole idea behind Injection Molding is that it is great for when you want to make high quanities of the same item over and over again. The initial costs are super high, but the actual cost of the item itself is very, very minimal. The general idea is that when you purchase plastic toy soldiers, you are mostly paying for the cost of sculpting and the cost of the molding. The cost of the actual plastic is next to nothing. The molds are made of high quality steel, and are very expensive. Add in the fact that it's primarily done in China, and you've got extra costs for overseas advisors and shipping.