I always figured you could build one out of pvc pipe and steel wool. Haven't tried it, but I figure it would work.
You can build one yourself with a form1 and $200. The PVC and steel wool would work a bit, but once you pay the tax you might as well do a good job. The tax stamp is only good for the one approved item, so a PVC one wouldn't be replaceable when it cracked (or blew up from the 357 pressure) I'm not trying to discourage you from doing it, I'm trying to encourage you to go all out and build something you would be happy with.
Buying is a better way to go for those who may not have the metal working tools. Think it through (silencertalk.com can help point you in the right direction) decide if you can build it, or if you should buy one. Buying "Class3" doesn't allow the ATF to enter you home as they please without a warrant (popular urban legend) and you can buy a dozen legally for less than you would pay an attorney as a retainer if you got caught doing one without the paperwork. I know you (Dee) are a law abiding guy from your posts, so please don't think I think otherwise, but that last point stands making because this is a public place and I want everybody who wants one to know how to get one and stay out of trouble. This is supposed to be fun.
A good place to start is to go register and post on silencertalk and ask about a good dealer in your area. That way members can post who you can deal with (and even who you DON'T want to deal with). A licensed dealer can show you some of the options, help you find a price and pick a caliber, and walk you through the reams of paper work. It's actually less paper than buying a car, but the approval takes a few months to come through. Once you have it, it's yours. No yearly updates, no nothin' but earplug free shooting goodness.