Hi there Mary,
That is a hard question to answer since there are many pieces of the exhaust system…and rarely do you replace them all and now a days you rarely even have to replace the muffler.
What I would recommend you do is visit a muffler shop and let them look at it. They can make most of the exhaust pipes, and they also sell universal mufflers and catalytic converters at a fraction of the cost of buying a new one from the dealer or auto parts store.
Most, if not all, general repair shops and new car dealers just buy new parts and install them, they do not bend and make the pipes themselves and that makes their prices much higher than a muffler shop will be.
Midas and Meinieke are two large brands you might have in your area, check your phone book or ask your local mechanic who they recommend.