Honestly, some of the popular brokers in South Africa have really high fees on their lowest account types. It is really hard to say one broker is best without actually understanding the requirements like deposit, which instrument do you trade etc.
Many SA regulated forex brokers like FXTM, XM, FxPro, Plus500, HFM, Vault Markets, Tickmill charge a lot on spreads with their Micro & Standard Accounts. So, I would say they are okay, but not good. For example, you would easily be paying 1+ pips spread on EUR/USD.
In general, in my experience, you should only trade with the South African brokers regulated by the FSCA. Here is how you can do it.
a. Check the forex broker's website for their FSP number.
b. Search the FSP number & license details on FSCA's search: https://www.fsca.co.za/fais/search_fsp.htm
c. Verify the license details & the products approved. Which will look something like the attached image in which Tickmill is an example. They are authorized to offer Derivative instruments as an Intermediary only.
d. Forex Brokers that offer CFDs are also required to be approved ODP. Search if the broker is approved as an ODP or not from: https://www.fsca.co.za/MagicScripts/mgrqispi.dll?APPNAME=Web&PRGNAME=Search_ODP
Note: I've only used the broker in screenshot as an example to search FSP, this is not a recommendation. I don't trade with Tickmill.