I am assuming you have a stock set up now. Cheapest option is just replace the muffler with the muffler of your choice to get better sound and flow. I have a single 3" system on my '01 with a Flo Pro muffler and I really like it.

 

Glasspack ????? 27.99 it's 26 inches and my stock muffler is 18 is that going to be a problem ?