(FORTUNE Magazine) – While a drought has scorched crops, killed livestock, and cost farmers in the Southeast $1 billion, growers in the Midwest are reaping bumper crops. From the taxpayers' point of view, the bountiful harvests are far more expensive than the devastation down South. The farm bill that President Reagan signed last winter was expected to cost some $54 billion over three years. Agriculture Department officials have now upped their figures to $26 billion for the first year alone. Independent consultants put the price tag as high as $35 billion. Congress hoped to reopen export markets for U.S. farmers by lowering crop prices to world levels. But farmers who agree to plant fewer acres are guaranteed an artificially high ''target'' price for what they harvest. They did their arithmetic and signed up for subsidies in unexpected numbers. Agriculture Department officials ask for patience. Says Ewen Wilson, deputy assistant secretary of agriculture: ''You have to give the program a chance. It'll take some time before we can really turn this thing around.'' Congress is likely to hold off until after the fall elections but then may summon the political courage to cut the subsidies back to more affordable levels.