E39 Vibration on Braking - help please !

I have vibration of the sterring wheel on braking on an E39. There's
no vibrattion through the brake pedal. Just had a diagnosis from a
garage - "brake discs (rotors) need replacing". On reading the Brake
FAQ I see that worn suspension bushes can cause vibration of the
stereing wheel. The vibration is worse at higher speeds. I would have
thought that warped rotors would be felt through the pedal as well as
the steerrng wheel. I'm on a tight budget, and don't want to replace
the brake discs unecessarily. Can someone confirm that warped rotors
would be felt through the brake pedal ? Or not ? I'd also be
interested in the difficulty (i.e. cost) of replacing the suspension
bushes *& which ones need to be replaced.

Its a E39 528i 50K miles.

Any help appreciated