$200/ mo asside from any payment you have if you don't do any of your own work. Basics are easy on these rides, oil changes brakes ect. The neat thing is that brakes almost never need to be changed compared to every other car I ever owned. The gm and japanese shit boxes I used to drive uses up pads every 25k, a bmw can go 80 if not tracked. And oil changes every 7500 (give of take depending on who you ask). A clutch should last 100k miles plus unless you can't drive a stick real well.
Your 335i is a little more to keep up with things like carbon build up, turbos and the like to keep an eye on. Water pump is a bitch too, pricey part and labor.
And I assume you are in your late teens/ early 20s.. At that age I wouldn't have been able to keep rear tires on a 335i. I had a pretty bitchin ride at that age and I had the same problem