By far your cheapest type of bet is to rent a Hyundai H1 bus from Avis at Cape Town International and drop it off at Skukuza airport. The drive will take you around twenty hours and with six adults you can shift that easily.
Book the rental from overseas and you'll get unlimited mileage and zero excess insurance, payable at point of collection. Don't speed, don't drive much at night and don't stop for strays. Carry your licence with you and be prepared to bribe any police you come across. They prefer it that way too.