Love mine - had it about 2.5 years now. The biggest bill I've had was to fix the leaky aircon (£1200). I'd advise finding a decent independent (I use BMWorx near Aylesbury) who know the cars and have a rather more competitive labour rate than the main dealer network.
I put about 20,000 miles on mine in the first 12 months (about 35,000 in total since i've had it) and can't think of many cars for similar money I'd rather have done them in. Granted the fuel economy isn't amazing (I average 19-20mpg) but having a decent amount of power on tap is lovely - you don't buy anything with a V8 engine expecting it to be cheap to run.
Ensure servicing all adds up, make sure the running in service was done, ideally buy one that's been enthusiast owned - odds are they'll have done stuff like changed the MAFs and refreshed all the fluids more frequently.