How do I travel between Fengxian District, Shanghai, Shenzhuang, Nanchang and Jiangxi and how much?

To be honest, I am a little confused by your question. Here is my general suggestion to my understanding:
From Fengxian Distr. to Shenzhuang, walk to Jiefang Road to take Shenhai Special Line to Shenzhuang MTR Station bus stop. It costs CNY3-5.

From your location, take MTR or public bus to Hongqiao Train Station to take a bullet train to Nanchang within around 6.5h. It costs CNY238 for a second class seat and CNY286 for a first class seat.

Thank you for the reply. It was very helpful.