Calculating the battery as given feels a bit like cheating for the 200$ number: A cursory search on Amazon puts the cheapest battery at 100€ and most in the 300

Calculating the battery as given feels a bit like cheating for the 200$ number: A cursory search on Amazon puts the cheapest battery at 100€ and most in the 300€ range. Quite unfortunate, as I had hoped the author found a cheap option.