Zero. In the first few years, they would likely trade grain and oil for hard money (gold, silver). Once that played out, much of the effected world would like

Zero. In the first few years, they would likely trade grain and oil for hard money (gold, silver). Once that played out, much of the effected world would likely have economies similar to the late 19th century--materials extraction, textiles, agriculture. The result would be a generation or two of poverty, but not a total collapse. Also, the "nuclear wasteland" business is pure sci fi.