is it a good time to visit china in early january. what is the average temperature in January.

The average temp in Jan. is around -5℃. It may snow a little then, but it won't have any effect on the Great Wall, so you can of course enjoy yourself on the wall then. The weather in Xian is kind of the same as BJ or a little warmer. It also is a worthy destination once you get to China.

I am expecting to tour china for 10 days. what is the approximate cost per day including attractions -- main attractions... in January. I plan to go to Beijing , Xian for 3 days, shanghai, and see the caves in Datong.

also I want to go to Tokyo from China. Are there any cheap flights that I can take from china/.

Can you give me some travel agencies which can help ?

Hi ruku, I think you can book through this website. It is a large travel ageny in China with a variety of itineraries, and they can help you dealing with your flight to Tokyo. Wish you a good trip!