I'm thinking the best application would be maritime surveillance. It takes a long time to get to the loiter zone, but once it's there it can circle indefinitely (I'm assuming it can be made unmanned). If you're ~1000 miles from the nearest airbase that's probably a lot cheaper than swapping planes out every N hours, and the $0.5 million cost is virtually nothing on a military budget.
not only navies use oceans - there are magnitude more commercial vessels that are currently forced to either use very unreliable low bandwidth or very expensive satellite communications.
I was suggesting it for surveillance, like the detection of smugglers, illegal fishing, et cetera. I can't imagine that it would be in any way cheaper than satellite communications if all you need is a communications relay.
I can't think of any good civilian uses, though.