pipes are very expensive so i will give u the cheapest 2 that actually give performance,
<font color=red><b>TERMINATOR</b><br></font>PRO RACE PIPE KIT - MTA2-HPP01
and this one
PB Anodized Pro Jet Pipe 47/49cc (Luck7) - A2-JETPIPE
if u just want to silence it, do the sparay can paint mod, but if u want a performance pipe get one of the above, the first one is for top end, the second one is for accleration, i have the first pipe and i was quite pleased with it, actually made by bike sound like a real 2 stroke, but the second one is quiter
and anothe best bang for the buck is the razor head kit from davesmotors