The weak Australian dollar in combination with high demand and changing fashions has meant a boom for sheep farmers, with wool prices hitting a four-year high. The average weekly price of wool hit $A8.21 ($4.28) a kilogram this week, up 25 cents over the previous week. Woolmark group manager Chris Wilcox said it was the highest price since June 1997 when wool prices peaked at 815 cents a kilogram.