Aftermarket Magnaflo converters are available for your car from O'reilly Auto Parts for either $219 or $312, they are relatively easy to install since they bolt on at both ends.
http://www.oreillyauto.com/site/c/se...gal&vi=1410376
You should also replace the O2 sensors, or at the very minimum replace the upstream one.
You'll also need a can of PB Blaster to keep the bolts from seizing up.