so i need a new exhaust..i think from the cat back..i just want to know what i should expect to pay. i went to monro and they quoted me that the assembly is going to be ~$700 and i just wanted to know if this is right or if i'm getting screwed.. specs: 1992, bmw 318i convertible.. no custom, no bells, whistles or thrills.. just wanted to know about the basics.. anyone?