Can you get Sealey in South Africa? If so, they are the cheapest I've seen. Just remember that you should have a dial guage to ensure the piston crown is at TDC. Personally, I'd be happy to change belts without the dial guage but you're better with it and its adaptor. From memory, the cam locks are £65, the dial guage is £25, and the adaptor is another £20 (+17.5% VAT). That is probably equal to the labour charge of having a garage change them though.