It does cost money. You should price some independent shops in your area as well as local dealerships. You will find that they both will charge more for labor than perhaps you are accustomed to pay. Parts aren't really that bad. All in all, I wouldn't call the maintenance prohibitively expensive. If you've been driving Accords and or Camry's, then you shouldn't see much of a difference. If you were driving a Yaris, then you will definitely notice an increase in maintenance costs.
I do think that people try to scare others away from BMW's without knowing what they are talking about. I am on my second 3 Series. The first one I drove while in grad school and managed to keep up with the costs incurred. That car has almost 200k on the odometer. When I was looking for a car most recently, I drove many different sedans: Altima, Galant, Pontiac G6, Charger, heck -- I even drove a Prius. I didn't feel as safe, nor did I enjoy the dirve as much. I went with another 3 Series. Over a year later, I am still very happy with my choice. All I have had to do is change the fluids and filters.\