Xiamen to beijing by train or flight ?

From XM to Beijing, there is only one train, K308/K305 and the train takes about 33 hours on the road. The train will not pass Shenzhen, let along stopover Shenzhen.
There are direct flights between them, but the price is hard to tell, because you may get a discount if booking early.
Last time, I order a flight with the price at around 500RMB. So it is suggested to go to the official websites of airlines. As I know, the XM Airline, Southern Airline and Air China have such kind of planes.