Hi, Gonsa,
In daytime, there are only soft seat D trains available and the train fare is ￥409.00 per ticket. For the overnight D trains, only soft sleeper are available an the train fare is ￥730.00 per ticket.
You will be on the train for about 10 hours.

As for the train from Shanghai to Hong Kong, it is operated every other day. The soft sleeper train fare is ￥935.00 per ticket in the 4-berths compartment and ￥1143.00 per ticket in the 2-berths deluxe compartment. The train journey takes about 18.5 hours.