Best option is to take some duty free with you and drink at your hotel. There are a couple of restaurants in Happo one where you can get a good noodle/rice dish for between 650-800 Yen (under A$10.00) or you can go to the supermarket and buy the instant noodle meals for about 250 yen. We found that the Lawson (convenience) store near the bus stop in Happo was really good, you could buy 1.5L Coke for 130 Yen and beers were quite cheap.
On the money front, we took cash with us and used our credit card wherever we could. The best place to get cash from an ATM is the 7 Eleven store in Happo.