How can I not get ripped off when I take my brakes in to get changed?

I have a 1998 Chevy Lumina sedan. About 5 or so days ago I noticed a grinding sound coming from from my front brakes when I applied them. I have this car for about 4 years now and I don't know the last time the the pads were replaced. I have called a few local shops and have got repair estimates ranging from $79 to one guy telling me $450! He claimed that the grinding noise means I need to replace the rotors as well as the pads. That doesn't sound right at all. So can anyone give me an idea of what this replacement should cost? I also heard to stay away from the national chains like Midas and Munro because they over charge.