Comms is 0.35% (market makers spread) + plus R57 for SBK doing whatever they do. At R100K positions the R57 doesn't seem significant, but if you then start wanting to build positions or take profit in smaller tranches, you slowly start getting bled - which I suppose is what banks are designed to do (hope I'm not coming across as bitter, but you need to keep this in mind). Watch out for the spread on some of the less liquid stocks (SBK relatively liquid so not so much of an issue), you can look at historical bid/offer pricing to get an idea of the spread. Also remember that when things get bumpy spread tends to widen significantly and this can significantly impact your profit/loss in the long run. Check out the SBK CFD brochure - they've got quite a few worked examples which can get you started on setting up your own model.
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