(This post was modified Dec 10, 2006 to reflect experience.)
I've been building 'chopper' mics this week; modified hand-held 'bullet' mics for my friend John.
I found a little-used type of mic (Shure 450) that has a much-desired element. Rather than take out the element and transplant it into an older bullet shell (fast becoming an expensive commodity themselves), I've built a few that utilize the mic shell the element is in. It has quite a different look than the old mics. I'd describe the traditional Blues Bullet (a JT30) as looking a bit like a '36 Chevy headlight. The 'choppers' I'm building look more like a '67 Polara. Anyway, John says he loves them (I like them, too), so the unconventional look doesn't have a negative effect on performance. The JT-30 types are on the left in the picture above; the Shure 450s are on the right (in the middle is my favorite mic, based on an old Shure DN50).
The other mic I'm working on is based on a vintage JT30 shell my friend Alan hooked me up with, and, just for fun, a Headphone Speaker as a mic element.
UPDATE: I tried the speaker/mic - it had a cool "AM Radio" sound, but was prone to feedback. I have swapped in a regular Dynamic element, and am working on "taming the beast" to hopefully use it on stage.
Why go to all this trouble? 'Bullet' mics with hot elements and a trick paint-job can cost over $300.00. The elements can cost between $50.00 - $100.00 if you don't know where to find them yourself. The vintage mics these are made from regularly sell for upwards of $100.00 online. The components that the mics are made of don't have to be so expensive - my 'choppers' cost less than $40.00 in materials plus a little labor; the experimental mic will cost a bit less when I'm done (of course I don't know yet how it will sound).