Exhausts systems ain't cheap, especially the ones that make power. My old Mad Dog slip-ons sold for $1,200-1,600 depending on the prevailing exchange rate.
This is the best bargain I've seen yet...
http://www.r3owners.net/threads/you-have-to-hear-this.20330/
Hell of a value, outperforms the stock set up, sounds great and very decent build quality.