The single jourey would costs some 200RMB.Generally, no taxi driver would like to take you to Badaling for single trip by meter, for they will undertake the expressway toll and there may go back to the city center with no one on the taxi. So, you can hire a taxi for round trip and I think it will costs 500-600RMB including the expressway toll. Talk about the price with driver clearly and pay at last in case of any matters happend on the way.It will take a bit more than one hour for a songle trip if there is no traffic jam.