Hi Peter,
I live in Japan and can tell you that the prices on the Japan Exposures website is pretty standard for prices across Japan. Despite the numerous products (film, paper, cameras, etc) that are produced here, they are more expensive here than just about anywhere else on the planet. As far as I know, there aren't really any discount places available, especially for new products. Two major camera stores (that are now mostly electronics/digital/phone) in Japan are Yodobashi Camera and Bic Camera. If you can navigate their sites (it's all Japanese but a translation program should help) you'll see that the prices are pretty standard across the board.
That being said, maybe others who live here might have know of some places that are not so well known.