As everyone has said Maz ...it all depends !!!
Taxis cost the same for one as two people. Stay local or walk and you can save quite a bit !!! ( as well as keep the weight down as a result of holiday excess

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A large Kingfisher averages at R70
A cheap eating place will cost less than R300, mid range R400-500, top of the range like Souymens or After Seven a bit more, especially if you decide such a fine feast deserves a bottle of wine plus brandy and coffee ! Then it's going to cost you about R2000 ( but you don't have to share the wine

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I think you can live very well indeed for £200 per week if you choose where and what to do with a little thought. A day out at say Morjim or Mandrem might well end up costing as much as a top meal so that's the night to eat cheaply etc.
I'm sure you'll have a great time whatever your budget. Much is possible for very,very little.
Happy Christmas
Dave