It was recently brought to my attention that some high level people are proposing that the IMO require a class of civilian (aka not military or law enforcement) vessels to use encrypted AIS to broadcast their position. This is an absolutely terrible idea.
Having ships broadcast their location encrypted defeats the primary safety aspect of AIS for those vessels, the encrypted messages do not expose their slot usage and thereby drastically increase the number of packet collisions in a local area (decreasing safety for normal AIS traffic), and encryption key management is not work well of large population of mariners. It would be a disaster in safety, technical and political terms.
The traditional "blue force" AIS units are just class A devices with slightly modified software (I own one). There really shouldn't be any cost difference. You could also change the programming for class B devices and have them transmit the encrypted position messages, but please don't do that.