Kim,
Obviously you can try to make your own muffler. But here's a couple more options:
1- Get a muffler from Mike Tyson or Cooper. These should drop the noise level down low to mid 90 DB. These will cost you 30-45 like mopartybob said.
2- Get a Jeronetune pipe. These are known to run in the low to mid 80 DB, very quiet. The original SS European version is pricey, but the aluminum ones from VooDoo props are much more affordable, whole setup goes for 155 including header/pipe/no-leak watercool flange/shipping.