I have some experience with getting nasty tones and the cheapest/easiest way is (if you're using a digital/computer DAW to record, such as Cubase, Garageband, or some other thing; remember, you can download a lot of similar programs for free off the web, such as Audacity and Reaper) to simply tweak the graphic EQ of the recorded signal so that can be turned into anything you want. Even if you record a clean or dry vocal track/signal, you can EQ it to sound like a telephone or almost anything super nasty. Another fix (if you're using something other than a laptop, like a portastudio or some other stand-alone device), get a cheap graphic equalizer (like a guitar pedal or something you'd use in your stereo hi-fi) and sweep that to make the vocal sound nasty. Otherwise, if you want to make a microphone that sounds nasty (for cheap), pull the mouthpiece mic out of an old telephone and wire that up to be your mic.
I really do like the other ideas mentioned above. I make my own piezoelectric transducer pickups, too. They are cheap and easy and you can attach them to anything that vibrates and you can amplify/record it. Put one of those on the back end of a can and record yourself singing into that.
I am just trying to think of ways to get this effect for low/no cost...
I love this thread, great discussion topic. I love the link to cranksturgeon.com, too. That will come in handy.

