I would agree with V8 on this one.
In terms of music stores in PTA, whereabouts in PTA? In Centurion, there is Bothners (Jean Village Music) in a small center on Jean avenue. In Menlyn, there is Oosthavens near the Metro in the center opposite Menlyn mall, and there is a small Marshall Music inside the big Pick nPay on Atterbury. There is another Oosthavens in Montana. There is also Musika next to the Makro in Silver lakes.
In Midrand there is Mitech.
I usually go to the Oosthavens in Menlyn for strings n things.
Regarding buying, my general rule of thumb is to go 2nd hand every time. The SAMIS group on facebook is a great start. Loads of gear for sale in the PTA area.