if I want to go to xian from Beijing can you inform me prices by train and flight

There are different types of trains and the price is different. You can check the Train Schedule here to check the specific ticket fare: https://www.travelchinaguide.com/china-trains/ . Well, the airfare is changeable. It often has differnet dicount. You need to pay attention to the airfare in real time. You can check the Flight Schedule on this website to find details.