What's the best way to find a cheap lens (good for portraits) for a digital camera?

I'm an aspiring photographer who's really into the artistic side of the field. I'm really into portraits and outdoor photography. I recently bought a $600 digital rebel xt but because i wasn't paying attention I didn't realize until too late that it came without a lens. So now i'm left with a camera with no lens. What's the best way to shop for a lens when you're on a low budget?

The Canon 50mm 1.8 for around $80 new makes a great portrait lens on a DSLR.

Not only is it one of the least expensive lenses available for your camera, it's also one of the sharpest.

craigslist ... You know what lens you need, you just have to be patient.

I second the 50mm f1.8 lens based from my personal experience. Not only it's great for portraits, I also found it pretty useful for low light conditions such as stageplay (if you're near enough that is), or candids as well.