CROS (Contralateral Routing Of Signals) hearing aids can be built in a number of configurations. Behind-the-ear (BTE) and In-the-ear (ITE) hearing aids can be wired together to allow the sound signal from one side of the head to be routed to the opposite side. Widex makes a wireless CROS hearing aid that uses a BTE hearing aid to send the signal and a BTE or ITE hearing aid to receive the signal. I understand that a FM signal is used to send the information to the other hearing aid. A CROS hearing aid is recommended when the hearing in one ear is very poor and a regular hearing aid will not provide clear and loud enough sound. As to the cost of CROS type of hearing aids they vary depending on the style, circuit and manufacture.