For $50, here:
http://www.giant-squid-audio-lab.com
Cardioid Stereo Microphone
$65 $55 SALE PRICED
Don't expect something great from these even in ideal conditions. You may like them if you don't mind editing afterwards but I would save your money.
I bought some of these. After replacing the mic elements and all of the electronics inside the battery box, these were great mics.
Actually, I bought the omni version and they weren't completely terrible. I made a couple of recordings with them and they were quite listenable. And seriously, after I replaced everything but the connector, the cabling and the battery enclosure itself, they turned out to be pretty decent mics. Looking back on it, it was a lot to pay for a battery enclosure, a connector and some cabling.
I think the original mic bodies were made from the body of a black BIC pen and some heat shrink, but it's a hell of a battery enclosure that comes with them! Since then, I've learned to make my own mics from information I got from the Yahoo Mic Builder's group. That's a time-consuming way of doing things, but you can learn a lot by doing it. On the other hand, you can get decent mics in the first place by spending a bit more money with the right merchant.