Terre Cotta is far away from Xian city proper. Tour line 5 and regular buses to Lintong County can take you to the Terra Cotta, which can be found in the east sqaure of the railway station. So, suggest you find a hotel in downtown. It will cost CNY100 to the airport and if you live around the Bell Tower, airport buses are easily to take you to the airport which is much cheaper. If you want to take a taxi to the airport, ask for the fare before getting in a cab. The same fare is needed from the downtown area to the terra cotta. Do not take a taxi there at the railway station. The drivers usually ask much more than it should be.