When it comes to mufflers, the 2 chamber Flows are loud. Both in and out of the car. I kept a set of Flows and a set of turbos that I would switch in and out occaisionally when the drone got old. Turbo type mufflers sound good in the car, but are not nearly as aggressive as chamber types outside.
Then there is always the tried and true glasspack type... It has a distinct sound and can drone in the car like chambers, but if you go with a good design, it will outflow anything less than open headers. Something like DynoMax Race Bullets flow like open pipe, and they are very inexpensive. Lesser glasspacks, like cherry bombs, have small internals and flow obstructing fins, so you have to do a little looking for a good set. Then again, I just named the best bullet type for you... DynoMax Race Bullet. They come in sizes from 2.5" to 4" and 12" to 18" bodies. If I was building a 2.5" system, I would get a set of 24219 bullets, 3", and cone the ends up/down to 2.5" pipe. That would slow the exhaust flow inside the muffler, taming the sound a tiny bit and insure totally free flow. That part is around $40 each from Summit or Jegs.
Good luck
Dave
Edit: The other good thing about bullets is that they are super lightwieght and take up very little space.