Actually, you've got a lot from which to choose. If you want performance, there are a number of alternatives ranging from $100 - $300+ in Flowmaster, Borla, and several other brands. If you just want a cheap replacement, your closest autoparts or muffler shop can provide help.
If you need to replace your entire exhaust system, most people here would recommend that you install a 2-1/2 inch pipe. There are any number of mufflers/tips you can put on. There are differences in the way they sound, and how they perform.
Hopefully, others here can give you some specific models for your z.
Good luck