It's REALLY important to try the first pair of shoes you buy on first as each foot is individual and certain makes/syles of climbing shoe are better suited to certain foot shapes. So, get an experienced climber to go with you and help you choose or go to a climbing shop and ask the assistant. Once you know your size and make, internet is a good option, as you can generally get beter deals than in a store.
If you are in the Cape Town area, Andy Davies shop, Mountain Mail Order, is really good and well priced. See www.mountainmailorder.co.za