German Chancellor Helmut Kohl has finally admitted this week what economists, bankers, and businessmen knew two years ago, when the West signed up to bail out the East: The tab for reunification is going to be colossal. Kohl is warning that new taxes will be needed to service an estimated $260 billion in off-budget expenses, including debt piled up by the Treuhand privatization agency, which the government must begin paying off in 1995. But economists predict the $260 billion estimate could rise as much as 50% by 1995. Kohl is using the fiscal crunch to put pressure on unions to cut their wage demands and on federal and state governments to pare back spending.