This is gist of my conversations with Bernelle about how much money one needs to have and move around. Feel free to edit/add/push the content to other places, so all and any praise or brickbats should go to him/er. All prices are in South African ZAR.
 Money to get from Airport to Conference and Back.
1. Getting to the conference - The recommendation is to have about R300 cash on you for getting from the airport to town (the city centre), or to the university in Rondebosch. You probably only need about R100, and we will try to arrange lifts, but R300 will cover you. But this is/was before http://lists.debconf.org/lurker/message/20160504.171932.8cc56301.en.html . If this is finalized then it will change things here.
 Staying in Hotels
While the University accommodation is the cheapest, if people want to move around then airbnb is well covered in South Africa (https://www.airbnb.com), and the cheapest hotels are around R600 to R1000 per night. R300 is possible but budget for double that (probably depends on negotiation skills as well as group bookings).
 Cheap mobile+Sim
The recommendation is to get a phone that can accept international SIM cards (no models,brands told or shared yet) , or budget to buy a cheap one (e.g. R100? - Bernelle checking on this, again no models numbers, brands etc. ) here, and a local sim card, and airtime, say, R100, This should also be taken with the information shared at https://wiki.debconf.org/wiki/DebConf16/Sim-card-information
 Getting around the city/country
For general commuting, R20 a day may well be enough, or you can get around for free with the Jammie shuttles. For sight seeing to other places you might need a car, and then the costs go up - again, make friends here to travel with! If you just stay for the conference, you could get by without anything.
 ATM and minimum budget to travel with (if just going to be in conference)
I think if you can draw money at an ATM - aka if you have a Visa or Mastercard, bring in R300, and not more than R1000 when you land.
 Food and Vegetarism
Food, you could get away with less than R100 for food per day, and more than R300 you're really going luxurious! Fast food places are more expensive that cooking for yourself, but an option if you can't cook where you are staying. They go about R50 - R80 per meal. I would recommend getting breakfast at supermarkets, as that is much cheaper. I would budget for R20 for breakfast, R50 for lunch, R80 dinner, so R150 for food per day. If you go to restaurants, this is more expensive, and if you buy food at supermarkets and prepare at home, this can be much cheaper.
We have a lot of vegetarian people, vegetarian meals are common, and often cheaper. The fast food chain outlets (e.g. McDonalds) I don't think have (good) vegetarian options, but there are many small cafes with really good vegetarian food, and the supermarkets also.
 Overall Budget for a short holiday (per day)
number would be, conservatively R600(accommodation) + R150(food) + R100(transport) = R850 a day. And I would say R300 for general cash, so that equals R1150 in all per day. You could stay alive with a lot less, this is decent.