Opening a can of worms, lets go for it.
I do business in the fuel industry, and as you are aware, prices vary according to magesterial zones, that being said, Uppington is one of the most expensive zones in SA but AVGAS there = R 10 excl/lt. Durban is a 1A zone, which means the "cheapest" and so is Cape Town, but in Cape Town area Avgas around R 14.50/lt. It comes down to 1 thing only - PROFIT to the license holder. Retail licenses is not dished out (exept if you are previously disadvantaged - for the youngsters, this is a term used to ride a wave of wich you were no part of before you birth

) so not too many outlets leading to the retailers thouht of mind "you want it, I have it, I make the price and whatever it is, you will pay"
I can go on for pages, but enough said..................
As a matter of interest, after the production companies to the endusers of petrol and diesel, there is a total margin of around R1/lt, with that R1 many costs must be carried and plenty people must try and break even or make a cent or 2 profit. Guessing Uppington not getting there transport for free, would be in the region of about 70-80cents per litre from DBN, that works out (@ 0% margin) to around R9/lt, you can do the maths to whatever you pay for your Avgas. (sounds like a profit of about R5 - R6/ltr - I WISH I MADE THAT ON FUEL, would probably fly a Citation Mustang then

)