Some good advice given here.
However stay the heck away from HI-FI corp and discount stores.
Autostyle is THE place to go if you want stuff, plus they overnight the stuff to you at a VERY reasonable price. For example the radio that bob posted is R200 cheaper by them. People say Mo sells cheap/ crap stuff......but the one time that I had an issue with something missing from a radio, he sent it through to me the following day.
http://www.autostyle.co.za/car-audio-1/car-mp3-wma-cd-players/pioneer-deh-1550ub-mp3-player-with-usb.html
I was buying from them when I still had my shop and that's ages ago. Everything I have in my 2 cars and my wifes car comes from his store. I've had zero issues with regards to quality. I swear by Pioneer and I've been running them for about the last 20 years. I've had MB Quart/ Rockford in my previous show car and I'm sorry, but it's over-rated for someone just wanting a nice system to listen to in their car.
Which corolla is this going in, because going 6 x 9 means that you're going to have to cut and the older model have a steel backboard, so you have to ask how far do you want to go? My advice, when you're in Pretoria drop me a line and I can demo my system in my double cab for you, it's got JBL speakers all round running off the radio with a small JBL 8" sub out back with a clarion amp. I'm a family man so I don't want the doef doef.....I listen to everything from barbie's greatest hits thanks to my daughters, to tuks for my wife and lamb of God for myself.
My advice, decent front set of speaker, 5:1/4", co-axels up front, (4" are just too small for front stage) , not splits, and maybe 6:1/2" out back. Or 6 x 9's if you want to cut. The latter does have a bit more bass. The radio will have no problem driving a nice set of speakers.
I reckon with a budget of about R1700, you can get a nice 4 speaker set up with a nice radio from Autostyle.
Stay the heck away from starsound, JVC, total rubbish.