i heard that dc exhaust was queit and if you want lots of noise apexi is the one for you.
check out youtube as there is always some one posting a video on there.
if not try exhaust.co.uk(cobra) in shefield as they will make you a custom stainless steel exaust and you can choose the sound! and last time i looked about £300 for full system and a decat
performance wise there is only a 3-5 bhp difference from the most expensive exhaust to the cheapest which you wont really notice