That $3k will get you an entry level, "assembled in the USA", Mac Pro.
You cannot deploy portable electronic devices on the submarine fleet without being absolutely certain there is nothing in it logging any data (sound, g-forces, pressure etc.).
Interestingly, the opposite is also true. The Navy SEALs (and everyone else) use consumer GPS devices because they cannot risk losing a classified M-code capable GPS device.
Even the reading times of the crew in a submarine would provide precious patterns.
Incidentally, should we consider this would be the cost of consumer electronics if we needed proper privacy?
And presumably because they can eschew many rules that others are bound by. If they wanted iPhones, they could probably get iPhones. They also often have black budgets and it is a real nice if you can sell to them. They release the money quickly, less red tape. Those deals are hard to come by though.