Ann: Gulf Secures Kupang Smelting Hub Facility Power Supply, page-40

$400/t is an absolute worst case scenario,electricity cost producing manganese from high silicon ferromanganese smelter slag. Depending on the purity of the ore the cost at standard Indonesian electricity prices is more likely to be in the range $200-$300/t. Still quite expensive. This is based purely off the 11c/kwh and some research on the net re arc furnace manganese smelting power requirements. Also assumes that your furnace is efficient I suppose.