Pretty sure, if some one can afford a M5, he or she will not have any issues forking out for an exhaust kit. So the cost would not be an issue.
Its usually the qualified technical support or lack of, in Pakistan which hinders people's ambitions.
I am based in Saudi Arabia and although, I have access to one or two of the highly qualified Bimmer Indys, I dont want to indulge in unwanted taking apart, unless its a pain I need to fix.
The EU and US has a lot of qualified and experienced mechanics, who do these jobs on a weekly if not daily basis. So people there are more willing to trust these work shops.
Check out my BMW E60 ride thread.