There's a video of a girls savage on YouTube.She has a universal muffler from JCW that sounds good.Not too loud,but good.
Dont know how much it cost though.Her husband works on hers.
And Ive mentioned it here but honestly cant remember if anyone commented on it.
I'll find the video link and put it up.
But I think the Harley Dyna muffler is pretty cheap.Or you can get them pretty cheap.
So Serowbot's suggestion is probably best.
But I did like the sound of the universal one