How much does it cost to change the caliper on a 1999 acord?

i brought in my car after hearing a grinding noise coming from my rear panger wheel for about a week. they told me the calipers were grinded and needed to be changed. they said that since the calipers on my accord alos deal with the emergency brakes that it costs more to change them. changing the caiper, rotor and break pad. it is going to cost me about $550 to fix this. is this right or am i getting ripped off, i dont know anything about cars and feel that this is soooo expensive, should i get a second opinion?