So far 42,000 miles I have had NO issues with my roadster, - Have owned Audi's for the last 20 years and have found them totally reliable up to 80,000 mile then things start going - I am expectingtthe same with the Crossfire. - get the warranty if can! I wouldn't touch ANY German car without it!
The only real expense that you could run into is the tires. they are not cheap - check tirerack.com for comp prices - but if you are looking at M3 you are in the same league. any Z rated tire isn't going to be cheap and don't really have a life past 25-25,00

Car is a blast - I would do it again in a newyork minute!