Xi'an Airport to Terracotta Warriors by Taxi - Cost?

What is the most recent cost to hire a taxi from the airport in the afternoon and take us to the Terracotta Warriors site and then wait for us and drive us back to the airport for a later evening flight? We will be only 1-2 hours at the museum. We don't have time to see anything else, just a quickie visit to take some photos of the warriors and then back on the plane. We can't join a tour since we don't have a lot of time.