Servicing 9-14k miles depending how hard its driven or every 2 years insp 1 & insp 2 can cost between £600 - £800 in a BMW dealership,tyres can be expensive if you buy them from a dealership but if you look hard enough or have mates that work in that enviroment they aint that expensive.I had mine a while ago & for about 55 quid i was getting about 340 miles roughly that was all kinds of driving.Front brakes are quite expensive but i never had to replace them in the 8k miles i done in it.Although braking from about 150 + there was a little thrum off them.If you weigh it up from cossie ownership & what you might spend in a year keeping them going all you really need to do on the m3 is service it properly with the correct oil (most important) rear coil springs are notorious for breaking best to buy new ones from BMW about £140 easy to fit undo the shocker bolt & lever it down.Then you get a 2 year warranty with the springs so not that bad & as long as its in the 2 year period there is no way they wont replace them,