i just got a new exhaust on my caddy (1980 fleetwood brougham) about 3 or 4 months ago, and a carburetor rebuilt about a month ago. here's what everything cost (i shopped around for the best deal)
Flowmaster 40 series muffler - $75.00
Catalytic Converter - $120.00 (i got ripped on this one)
Chrome Tip - $5.00
Complete new pipes (from headers down... i still have stock headers) - $45.00
Installation of the above - $50.00 and about 15-20 minutes of work.
Rebuilt - $215.00 (including labor)
i'm sure you could get a better deal getting it rebuilt, but i was in a hurry.