These are way more expensive than I expected. Prices between 50–80 USD for what amounts to a wall-wart tethered to a battery-shaped piece of plastic with metal

These are way more expensive than I expected. Prices between 50–80 USD for what amounts to a wall-wart tethered to a battery-shaped piece of plastic with metal contacts. Amazon has similar products in the 10–20 USD range. Still a lot of money, but far more reasonable.