HELP!! I got a serious brake problem

[junia]

I took my car into the local brake shop to have it checked because I'm having problem stopping.  I'm thinking maybe a quick fix you know, 40 or 50 bucks even a 100 if it was something crazy.  The guy gives me an estimate of 470 dollars.  He said that I needed a new mastercylinder and new rear brakes with new roters.  Now from past experiences in Japan, I've been able to pick up a master cylinder rebuild kit for about 20.00 dollars or even snag on off of a car in the junkyard for about ten or so.  Are they that expensive that I need to pay 400 bucks to get all that done?  I'm pretty sure rotors aren't that expensive because I see them for under 100 a pair around here and there.  Can someone give me a break down of how much the parts would cost me because I'm just going to get off of my lazy ass and do it myself.