And they never even account for the costs of the person's education or years of experience.
They don't list the cost of the the facility where a project like this can be built without being rained on.
Or the health care over the years to ensure that one's hands and mind function adequately for the task.
They don't even account for the cost of the calories of food required for thought and motor control.
This project would actually cost >$1,000,000
Seriously though, if you are committed to a hobby, there are many projects that will be much cheaper for you than for a person who has not yet entered that hobby. It is normal to only list consumable components in the list of prices. Tools, for example, are a sunk cost and not consumable so they are not listed. I often see this frustration from visitors to hacking and hobbyist sites. People who are upset that getting into a hobby requires an upfront investment in time and money that then makes everything else cheaper.
That said- I agree that the rPi and amp should have been listed. Even if it is likely that a person would have an rPi around- it is still consumed by the project.