Avis has longterm car rental and for +- R4000 a month you'll be looking at a Chevy Spark with no power steering.
It's a little bit stupid, I won't recommend it.
Depending on how long you want it for/don't mind the crappy car, I'd recommend maybe leasing a car from a place like Ariva. I'm coming up to year 5 next year and will be purchasing the car from them (For 33k), but I haven't had to worry about services/tires/insurance or getting a loan against my name for it.