They have their own off-road H-pipe for around $100. This would match up nicely to the Flowmaster American Thunder system they have for ~$300 if I remember correctly.
The only 2 parts of the exhaust that you need to do at the same time are headers and mid pipe. But that's only if you ever want to go to long tube headers (or Bassini mid length headers). Otherwise you can do every component of the exhaust piecemeal.