You're better off just skipping by the likes of the EX71 and even the CX300. If you still want to stay in the $30 and under there are better choices. Try searching, not just here but the web also, for Creative EP-640, maximo IM-390, Meelec AI-M2 for a start at or near that price point.
They're both decent for their respective prices. There's a lot of fakes of both floating around. IMO it's worth spending a little more for better sound quality. In the last year, I've gone from Panasonic HJE-50 earphones to Alessandro MS-1s.
Be careful, Headfi is a dangerous domain. Primarily for the wallet, as many here will attest.
I'd go with some Audio Technicas from audiocubes myself. They'll blow the EX71s away. I have the EX90s and they're actually outstanding phones. I haven't tried any high-end Shures or UEs yet, but I'll get around to it eventually.
EX71s are not produced now so it's pretty hard to get genuine ones.
Besides, they are not durable: mentioned above problems with cable. Im my case cable was in perfect condition. Nevertheless, right earphone just stopped working after a year.
EX71s sound quite similar to CX300s, differences are minor.
Better bang for the buck are EP630s: they sound pretty close to CX300s and are much cheaper.
when i had them, i thought that they were fine. yes the bass is somewhat bloated and they didn't isolate as well as true a iem but it's not like they were total crap like some here make them out to be and they're not true iems either. they're canalphones. compared to others out there like koss plugs or marshmallows for example, they were pretty decent. at least they didn't sound muffled. at the end of the day, it's what you enjoy that's most important. if you have an opportunity give them a try. it's what head-fi is about, trying different cans and enjoying your music.