There are a million backpacker hostels out there, (well, not a million, but a lot), just do a search for them or buy a good backpacker guide for that area. There is a bus that drives from Capetown over Durban to J-Burg, and stops at all hostels along the way. When you are down there it is easy to get the information directly at the place.
Also what my mother usually does is just drive in her rental car and then look wherever she is for something that looks nice and asks for the price. She often gotten from people in restaurants and such tips about cheap but nice B&Bs, another source were guidebooks, those aimed at people touring the country by themselves.