I made a quick chart of parking price vs days parked for various options, including getting an Uber Taxi or MyCiti bus from Cape Town CBD to the airport.
- Shaded parking in P3, P4 is cheapest up to 5 days.
- Long Stay parking in P5 is cheapest up to 12 days.
- And then Uber to the airport and back is the best option.
Interestingly, the Katanga Valet parking (which includes a wash, vacuum, polish) is not much more expensive than the Garage parking (in P1, P2.) Having used them before, I'd recommend it - especially if you are late and just want to dump your car and run to the check-in.