A great advantage of priceline and other online booking services such as hotwire and travelocity is that they quote you a price, even in Japan, for a double room, but the pricing is often in the single room range. Thus, at a decent Tokyo hotel you can save quite a lot. I stayed at the Dai Ichi Annex in the Ginza area for around $120 a night for two last year. The double rate was lots higher.