Can u recommend a hotel below RMB 400 around Tourist attractions area in Beijing which is nearby to Metro station and easy to take taxi.

The local Days Inn Forbidden City BJ at No.99, Nanheyan Street, Dongcheng District is suggestd for you.
The fast train? You mean the trains from BJ north railway station to the badaling?
if so, you can walk to the tiananmen east station to take the subway line 1 to fuxingmen station and then change to line 2 to xizhimen station. Get out of the station from Exit A1 and you can find the BJ north railway station.