Quick answer: Cape Town runs about EUR 75 per day mid-range - noticeably less if you eat local and walk. Cheapest window: November–March (summer, dry).
What things actually cost
flat white at a specialty cafe
2.00 EUR
craft beer at a taproom
2.50 EUR
sit-down dinner main course
9-13 EUR
Uber across town
3-5 EUR
Table Mountain cableway return
about 22 EUR
glass of local wine
3 EUR
Eat well for little
Gatsby sandwich - a massive Cape Town-only sub stuffed with fries and masala steak, around 5 EUR and enough for two
Cape Malay bobotie in Bo-Kaap - spiced baked mince with egg custard topping, about 8 EUR at a local canteen
Neighbourgoods Market at the Old Biscuit Mill (Saturdays) - graze on everything from bunny chow to oysters for 10-15 EUR
Truth Coffee on Buitenkant Street - steampunk roastery often ranked among the world's best cafes, flat white about 2 EUR
Braai platter with boerewors and snoek at a Kalk Bay harbour spot - grilled fish straight off the boat, 10-12 EUR
Money mistakes to avoid
Going up Table Mountain without checking the weather webcam first - the 'tablecloth' cloud rolls in fast and the cableway closes in wind, so go the first clear morning you get
Hailing street taxis or walking long distances after dark - use Uber door to door instead, it is cheap and the standard here
Not renting a car or booking a tour for the Cape Peninsula - public transport barely covers Chapman's Peak, Cape Point and Boulders Beach
Visiting in December-January without booking ahead - it is peak local holiday season and prices for stays and restaurants jump sharply
Transport without the tourist tax
From the airport take an Uber to the City Bowl, about 20 minutes and 12-15 EUR. In town Uber is the default and rarely costs more than 3-5 EUR per hop; the MyCiTi bus works well along the Atlantic seaboard for about 1 EUR a ride.