cheapest will be Uber
Best is take the train from Sandton station which goes directly to the airport.
The concierge will arrange a car to drive you to the train station free of charge. Takes 5 minutes and the train will take 25 mins to reach the airport.
Use Guatrain from Airport to Sandton City Station. The Hotel is within 7 minutes walking distance if you do not have heavy luggage .
1)Call hotel concierge and ask for pick up
3)arrange taxi inside the airport (not outdoors)
Get an answer from Sandton Sun staff and past guests.