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The FMF universal two-stroke muffler that Spud uses on his Zong would likely be a good choice at a fair price.
YamaZong XT200GY-2 gets an FMF Turbine Core 2 Spark Arrestor
I tried to modify the Beast performance muffler, and it was more trouble than it was worth. The stock steel muffler from a first generation beast can be easily modified, but it requires a welder.