This is a reasonable cost breakdown of our first prototypes. As we scaled up, some costs became much lower and others actually increased. For example, we move

This is a reasonable cost breakdown of our first prototypes. As we scaled up, some costs became much lower and others actually increased. For example, we moved from hobby-grade to EV-grade batteries, because we found hobby batteries tended to be less stable and reliable. Our costs include parts, labor, and many of the costs that others mentioned. For example, having a warranty or a return policy are costs that scale with each unit. You're correct that you can build something with similar performance (if not reliability) for cheaper, if your labor is free. Endless-sphere.com is one of many resources if you wish to do a home build.