All cars are expensive to maintain these days... Whoever said a major Mercedes service (B Service) costs R800-R900 is smoking some strong stuff. (Or maybe that's on the service plan?) I've had 2 of those done so far and they were R5000 and R9000 respectively. An "A" service is about R2-3k. That said, I used to have a Jetta and even a small service on that was never below R4000 either. Mercedes parts are some of the cheapest I've seen (cost R1200 for an alternator a few years ago, vs a few grand (I think R4000) for a Toyota), but their labour rates make up the difference. Volkswagen, Toyota etc. tend to charge insane prices for parts but their labour is a lot cheaper. A colleague recently had a major service done (including replacing a cambelt) to his Land Cruiser and it was just under R11k.
With especially German luxury cars with lots of electronics, sensors, computers etc. it's best to go to the dealers since they know what they're doing and what to look for. Don't know about Audi's but with Mercedes dealerships you get fantastic service as well, and if they didn't fix your issues they will get it sorted without charging more and telling you sob stories. As others have said though, it's much cheaper with a service plan on a new car. Of course, then you're paying a few thousand every month for years on end anyways...
With especially German luxury cars with lots of electronics, sensors, computers etc. it's best to go to the dealers since they know what they're doing and what to look for. Don't know about Audi's but with Mercedes dealerships you get fantastic service as well, and if they didn't fix your issues they will get it sorted without charging more and telling you sob stories. As others have said though, it's much cheaper with a service plan on a new car. Of course, then you're paying a few thousand every month for years on end anyways...