Naively searching for every lines of the bill of materials gives me around $300, with a handful of items being around $50 and everything else under $5. I’m sure a hobbyist could find the parts for cheaper, especially things like individuals connectors that I found for around $5. I’ve seen them go as low as $0.25 when bulk purchased.
Disclaimer: it’s possible that some SKUs led me to the wrong products. I am not into electronics. I encourage you do to the same exercise before drawing conclusions.
A post from the hackernews thread had a lot of that info: