Pulsation while breaking .

[Boos2006]

Hi All,
I have a 05 X5 4.4 lit are recently I started getting pulsation or bubbling when I apply brake. Car has about 100 KM and I had recently changed all the tires. Tiers are properly balanced and alignment is fine as well. Initially I took my car to a mechanic and he told me that I need new brake pad in front (as they are low) rear pads can still do as they are 4mm left.
In my area BMW dealerships are running promotion on break jobs ($434 for front brake installed, new pad, rotors and sensor) I decided to take it to them. BMW dealership is now saying that there is a problem with my caliper and my front brake pistons are ceasing. They can rebuild the cylinder in the piston at the fractional of cost of original but this will still cost me $800. They have refused to do only break job without doing caliper.

Pulsation problem is intermittent and happen only on speed access of 120 KM at lower speed breaks are fine.
You guys are been great so far, please help / suggest what I should do . I don’t mind spending money if this is what need is but I have a strong feeling dealer ship is trying rip me off.