I once thought of modding that underbelly exhaust can from LeoVince than I imagined the amount of work put on it to make it perform well as stock:
-New pipe (if you want to keep the stock thing): 130$ (in my place probably cheaper but I will give the US price for better calculation)
-Custom-made chamber (it's the big box-like mid-pipe on big bikes like the CBR1000RR or CB1000R). Reason for having this thing is to keep a little back-pressure up AND the noise down. Trust me with the sound part, you don't want to hear it scream at 7-8k rpm everyday after work. Price will varies, if you have access to a CBR150R mid-chamber, go for it, it's small and compact and really does the job well on the 150cc machine.
Here it is, the black box before the exhaust can
-The LeoVince can: 500$. may have to add 50$ for labor retrofitting stuff to "hang" it under the bike.
-The fuel control unit: why, you may ask. It's because you've just changed the exhaust into a full system: 300$. You can calibrate the thing yourself but it's best to leave that to a professional. NOTE: this does not include dyno fee or labor time.
-This is optional (I think): new airfilter for the added thirst for air of the new system ~ 10-20$
The total is almost 1000$ solely for the look good effect on a 5000$ machine. I'm not trying to talk you out of this, I simply state my opinions. I welcome modders because they can do what I am too afraid to do. Hope you find this informative.