what is the taxi fare from Xian airport to the new Westin hotel

It will take you about 150 RMB to arrive at your hotel.
I advise you to take the shuttle bus line 4 from the airport to Xiaozhai and then take a cab to the hotel. It is much cheaper than taking taxi directly.

Many thanks Michelle. There are 3 of us, so probably easier to just take a taxi from the airport. BTW, we will visit Xian on or about 15 October, wonder what the weather is like?

If you have 3 people, you can choose to take a cab, but the shuttle bus fee is still cheaper. 26 RMB for person is the price of the shuttle bus.
October is a good time to visit Xian. The weather will be cool and the average temperature is about 19 centigrade degree. Long-sleeve shirts, thin coats and thick coats are all needed for the changeable weather in October. Take it easy about the weather and enjoy your trip.