ST Discovery Boards are a far cry from the $40 this supplier is asking. You can purchase it directly from ST or one of their approved vendors for around $20. The board itself and the free development environments are very good in their own right and a great way to get into 32-bit ARM programming once you've outgrown the Arduino. (But it's easier to start with a low-power STM32F1-based Blue Pill board.)
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