I went to Okinawa, and lots of things happened. But first I wanted to tell you that Okinawa is pretty easy to get to. I booked a flight two weeks in advance, just ahead of Golden Week (but not during GW), and my tickets on Skymark were 27,000 yen. That's cheaper than most round-trip shinkansen tickets. With more advance notice, it could be less. I feel like people are always taking ANA or JAL and bitching about how expensive it is, but I find that the domestic cheapy airlines have better deals. They fly from Haneda and the flight takes two and a half hours, which goes by pretty fast unless you have rowmate issues.
Burney's Breakfast, where my friend and I shared a twin room, a small clean white wooden room with loft beds and Ikea furnishing and a computer and wi-fi and breakfast included. It was about 2,000 yen per person per night for this.
There's a monorail in Naha that takes you from the airport into town and goes up to Shuri Castle, so for Naha stuff, it's more than adequate. But the bus system for the rest of the island kind of sucks. It doesn't come that frequently and takes a long time to get anywhere. For exploring outside of Naha, next time I would rent a car. The hostel recommended this car company, and it's really cheap: as little as 3,000 yen a day for a compact car, all inclusive. They're located in Okinawa City, and while they will bring a car to your hotel for you, I definitely recommend reserving at least a day in advance, since it's difficult to work out the delivery logistics otherwise. And all the best beaches and nature are outisde of Naha.