I would say pads and rotors is a more likely scenario.  Can you stop ok?  Does your pedal feel mooshey?

Werd ... I'd try the pad change and the rotors ...Truthfully I'd change them myself 

WHATEVER mechanic told you it was the master brake cylinder should be punched in the mouth for being a sheister. IF it were that it wouldnt make noise, just make stopping almost non existent. He knows it costs more to replace that so he'd probably replace it, charge you a crap load for labor, just to have you come back the next day saying the noise was still there and he'd THEN do the rotors and brakes. Please dont ever go back there. My dad's been a mechanic for over 25 years and he'll say the same thing. If your changing the rotors get drilled slotted and some nice pads (dont use ceramic with those) use raybestos or kevlar.