Thanks for all your replies! The cheapest option for me would probably be to use returning flights and stay one night in Narita between the flights. The flights on
http://www1.tour.ne.jp seem to be all around 29,000円 (USD 323)--but I haven't figured out yet if they will accept credit card (I am still not that proficient at reading Japanese
). The flights offered on dohop.com are around USD 400, so I may use those in case I cannot book them on the Japanese site.