Hat did the populist party support in order to fight against high costs?

The correct answer is that the Populist party demanded government ownership over railroads to reduce the high costs.

During the 1890s the confrontation between the Populist party and railroaders was at its peak in Kansas. In its party convention of 1890 in Topeka, the Populist party members demanded the government should exert his authority and became the sole owner and operator of railroads in the United States. From then on, Populist candidates in the state of Kansas ran campaigns expressing that the government should control railroads, as the only solution to the problems with farmers and businessmen in the high planes.