Just a quick story on this.  I had the same problem over the summer when my tailpipe finally rusted off and I went to my local Midas shop.  They wanted something like $250 to replace the muffler and pipe.  I told him to just weld on a new tailpipe since the muffler was still OK.  When my new tailpipe fell off about 2 weeks later during a road trip I went to a muffler shop in Asheville, NC and the guy went in the back and brought out a nearly perfect match for the original muffler.  He then bent a new tailpipe and welded everything together.  Total charge was about $65.  All is fine and quiet. If you're near Asheville, I could tell you where to go.

Gerry Royston
Bethesda, MD
1987 Westy