no conversion kits but a muffler shop should be able to do it for you.
just make sure they have the machine that bends the pipes so you're not getting ripped with the premiums from a muffler shop that buys its parts off another muffler shop or company.
Mufflers are your choice but, I recommend the setup that I have.
True duals with Pypes Violators mufflers
Garages > Schumi23's 1998 Ford Mustang - FQuick.com
If you're looking for mufflers relatively cheap, go to eBay, they usually have some great deals on them.
Recently I saw Brenspeed selling the mufflers I have for $110. (I got mine for $50 though brand new).
Let me know if you have any more questions, and welcome to AFM by the way!