The Institute for Supply Management’s March manufacturing index slowed and costs rose to the highest since August, ISM said Monday.ISM’s factory index fell to 50.9, from 52.3 in February. Readings above 50 indicate expansion.The index measures U.S. manufacturing activity. Economists had predicted the index would decline to 51.4, Bloomberg reported.“A positive for March is the customers’ inventories index . . . which is a possible indication that manufacturers’ inventories are nearing satisfactory levels,” said Norbert Ore, chairman of ISM’s manufacturing survey committee.“On the negative side, prices appear to be surging for certain commodities in the face of slower growth,” he said in a statement.The prices-paid index jumped 6.5 points to a 65.5 reading, the highest since August.