Mechanical watches. Most people don’t understand just how expensive they can get, outside of the ones with diamonds all over them, nor why they’re so expensive. Most people also don’t understand how expensive it is to be allowed to buy certain models, depending on the model and the dealer you’re buying from. Also, watch repairs and regular servicing of mechanical watches is something most people don’t consider, and the price of tools if you want to do it yourself can be very expensive and require a lot of skill.