Casio Watch 問題 20 marks

Sorry I cannot type Chinese, but I'll still answer your question.
The price of this watch varies depending on vendor. It probably costs more in City Chain stores, but less in stores in Sino Centre in Mongkok. Sorry but I do not know the exact price of it.
Your best solution is to contact Javys International for their pricing first:
http://www.javys.com/casio/series.php?series_id=GS0014
http://www.javys.com/casio/contactus.htm
Then you can compare this price with those at Sino.
You can also try asking Javys for a list of dealers near your area that carries this watch model.