Hearing aids cost about the same as a high quality stereo sound system. The high cost results from having to miniaturize the components. Imagine how difficult it is to make microphones and speakers which are small enough to fit into the plastic cases which can be worn on, or in, the ear. Hearing aids are only fitted when there is no available medical treatment or surgical procedure to correct the hearing loss. And the cost of hearing aids is much less than the cost of surgery.
Hearing aids require special batteries.
The batteries are extremely small and usually cost about the same as the batteries used by a flashlight. Batteries may last from a few days to a few weeks, depending on the type of hearing aid and the amount of time it is used. Hearing aids need very little special care. Hearing aids are built to be durable, but, like any electronic device, they can be broken if dropped on a hard surface. Water can cause damage so they must not be worn in the shower or when swimming.