everyne says that control arm bushings need to be changed but what about
thrust arm bushings? should I change them too at 45000 k?

The only reason to change the control arm bushings would be if they've failed. One symptom of that is a vibration under braking at 40-60mph. However, since there are other possible causes of that a proper inspection of the suspension is called for before randomly replacing parts. This is a case where professional diagnosis could well be cheaper in the long run. You'd want to use a shop with lots of BMW experience because they'll know what to look for.

thejlevie is correct, however one thing is worth mentioning here. there is a control arm and tension strut on the front end, but they are also called lower and upper control arm, thrust arm.

tension strut=thrust arm=upper control arm
(real) control arm=lower control arm

so when you hear someone talking about changing the (control arm, thrust arm) bushings, they mean tension strut bushings. control arm (lower arm) already comes with the bushings as a one assembly.

The only reason to change the control arm bushings would be if they've failed. One symptom of that is a vibration under braking at 40-60mph. However, since there are other possible causes of that a proper inspection of the suspension is called for before randomly replacing parts. This is a case where professional diagnosis could well be cheaper in the long run. You'd want to use a shop with lots of BMW experience because they'll know what to look for.
you know how much does a dealership charge for it?