There is more to a performance exhaust system than just the physical fit.  There are additional costs and characteristics that you need to be aware of before you fit a performance system.

You need to be aware that your fuel system and timing need to be tuned to the exhaust system.  To do this on a Fuel Injected Motorcycle requires alterations to the Fuel Maps and Spark tables in the ECM (Electronic Control Module).  These need to be done dynamically and they require software to install or alter the data.  Without this, the performance system is likely to run poorly and there can be throttle and RPM ranges where the engine may run lean which may overheat and damage the motor.  The stock system is pretty clever, and unless you choose a good system and map it correctly the standard system may provide better performance in useful rev ranges.

Another thing to consider is that most or at least many performance exhaust systems are made for race use only.  They may exceed noise limits, and  not be legal for street use.  A level of noise that you think is OK on someone else's bike may not sound so OK once you convert your bike.