A lot of it is self-maintenance in fairness, so limited labour costs - they're generally a fairly easy car to work on as you know and at the age they are now, there's plenty of used spares knocking about as more & more cars are being taken off the road.
An example - a couple of weeks ago, I replaced the alternator - just under €150 for a new (not reconditioned) Hella unit - I'd shudder to think what something like that would cost on a 530E tbh.