Sir, so far as I know, the cheapest way is taking train, but it will take you around 19 hours from Beijing and 17 hours from Shanghai to Fuzhou.

If taking flights, it will take shorter time and there are always some discount tickets. Since last time I flied from Shanghai to Fuzhou, and it only cost me CNY600 with the 36% off airtickets.

Thus, personally it is better for you to take flights.

hello ms elena,
i check the air china, they dont have direct flight from shanghai to fuzhou, it will either has to have one stop connection or two stops connection, and the fare is ridicurios, very expensive. more expensive than the ticket that i fly to china.

From Shanghai to Fuzhou:
There are flights from Shanghai Pudong to Fuzhou provided by China Eastern Airlines till August 08, 2009. There is no flight information from August 09, 2009 onwards maybe the airlines have not announced the schedule. If you prefer to depart from Shanghai, you would better wait for a few days. At present, the full airfare of economy class seat is CNY780. You can take it for reference.

From Beijing to Fuzhou:
At present, there are many flights from Beijing Capital International Airport to Fuzhou in December. But the full airfare of economy class seat is CNY1,550, almost 2 times of the airfare of Shanghai-Fuzhou flight.

ThankS mr Yang.