Went through a similar exercise looking for a bike for my son. Sadly, R7k does not get you much. Bike prices have simply sky rocketed of late.
I was fortunate enough to have picked up a really well looked after second hand bike for R5 500. They are there, but you have to find them.
I agree with you, new is a better option for people new to the sport. The bike shop will make sure they are set up and of course you get a warranty.
For your budget, value for money is your primary concern. Brands that offer this are Titan (probably the best at the moment), Silverback, Merida and Axis. Many people won't agree with me, but Avalanche also has some good value propositions.