My 2000 530i cost me roughly £1300 over just under 18months of ownership, mainly brakes, tyres and chasing an intermittent power loss issue (which on reflection was probably just the early signs of its ultimate head gasket failure) which involved changing the MAF sensor, cam & crank position sensors - more than once - and one major service, not bad given I only paid £1550 for it and still got £500 back as spares or repair, in the grand scheme of things I still think it was a relatively cheap way of running such a car for that time all things considered.
It could easily have cost me more, and would have done so had I fixed its head gasket and the gearbox fault that ultimately did for it but in the end I decided enough was enough.
I'd dearly love an e38 740i Sport next but am after the e39 experience I'm alas only too aware that an e38 would be no better in terms of niggly and / or expensive problems and am left pondering if it's worth the bother, probably not much as it pains me to say so, I see why Fox retired his e39 - which I'm sure is a much better example than mine ever was - they reach a point where they are more trouble than worth bothering with....
What I ultimately replace it with now I don't know, I'll probably end up sticking with the diesel Corsa I've bought as a stop gap for longer than initially envisaged.....