You can get a nice local one for around 3,500... many local mufflers in this range are glasspack mufflers with smoother sound and better tone than 800 peso mufflers... still pretty loud, though.

You can get a sports muffler with good tone secondhand at Banaue or Evang, expect to pay up to 5000 for secondhand 5Zigen, HKS or RSR, but be wary of rust.