If you can't read Japanese, then use
Google Translate or Firefox +
Rikaichan to scan the deals at
ToCoo.jp. It's a new site so no idea how long they'll last. Some of the hotel and
ryokan are being off-loaded as low as 109 JPY per night; often these are deals for the following night. You won't find Y109/night deals if you try and book several weeks in advance, but you should be able to still find rates at 40 to 70% discount.