Cost for custom built exhaust Honda NSC50R motor bike?

Hi, I want someone to build me a custom built exhaust for my moped and was wondering how much it would cost. It is a Honda NSC50R 4 stroke moped. Also, do you know how much the speed will increase with it?

Custom exhausts usually run about $1,000.00 and usually don't increase speed but rather responsiveness if used along with a breathing air filter and re-jetting.

UK forget it as it would then not conform to Moped legal definition and you would have to get it Legally Re-Registered as a Group A1 Light Motor Bike and the A1 Driving test must be done on a bike of at least 120 cc

Andy C