Land prices skyrocketed in Japan last year, with the choicest piece of commercial real estate selling for more than $6.7 billion per acre, the government reported Friday. Japanese newspapers bemoaned the record price jump in Tokyo, where residential real estate land rose 68.9 percent last year, nearly twice the previous high of 35.9 percent in 1973 and almost triple the increase in 1986 of 23.8 percent.