It's less than 1 hour, or about 160, to take the Third Ring Road directly from the intersection of Guanshan No.1 Road.
1 You can take the airport bus if you are not in a hurry. There seems to be a bus starting point in Optics Valley Gymnasium of South China University of Technology, and the time seems to be 1 every 1 hour. Please call the airport to ask. It will take about two hours, 40 yuan.