Chances are $200 is not going to buy you much at the muffler shop. At most it will get you something that end up looking pretty cobbled up. The shape of the e34/e32 muffler is a major pain in the ass. There is an e34 M5 muffler on ebay right now for $99. There is also a guy selling a new Bosal 535i muffler for $140.
http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW
BMW factory exhaust is pretty efficent.