First, just tell you although Lushan Mountain is in Lushan City not in Jiujiang City, it’s easier for you to get to the mountain from Jiuiiang. Staring from Jiujiang Railway Station, it may takes around 1.5 hours to get to the mountain. You may take the Bus No.1 to get to Jiujiang Long-Distance Bus Station from Jiujiang Railway Station and then take the bus at the bus station to go to the Lushan Mountain. The ticket is around CNY9 (I am not sure whether the ticket cost has gone up.)