Aniplex's pricing is outrageous but I would never compare Anime pricing to HBO or other American TV show pricing. There are too many variables (or lack there of) that go into the influencing the pricing of Anime that isn't relevant for HBO or other American shows sold in the US. For example ad revenue helps offset the cost of releasing American TV shows and American studios don't have to pay licensing fees to themselves. Also, considering even mediocre TV shows will likely outsell the best anime just due to exposure, economics of scale/supply & demand/etc. let them get away with cheaper prices.
HBO shows have zero ad revenue