If you're talking a knife for self-defense, don't limit yourself to $30. Yes, a $30 knife can kill you. It's another thing to INVEST in one knife, versus stealing or finding whatever a thief can.
For $30 though, mabe a Gerber, or something by Columbia River.
I prefer Syderco and Benchmade.
Log on to
www.bestknives.com for pictures, specs, and some good prices. I'd look for something in ATS-34 steel, and a rust-resistant coating. I prefer thumb hole openers. If you like thumb disc openers, or thumb stud openers, look at Ken Onion. His "speed safe" is very fast.
Plan on spending $80-$100 for the knife, plus another $12-$20 for some sharpening implements.
BTW, if you plan on stabbing bone, folders aren't always the best choice. You want a small fixed blade, like a Benchmade Nimravus or, my favorite, the Camillus CQB2. Of course, those come with small belt sheaths, not belt clips.