$30 and under - Kershaw Leek (assisted opening), Buck vantage select (small and large sizes), Kershaw Skyline, Kabar Dozier, Kershaw Speed Bump
$60 and under - Spyderco Delica(3") or Endura(3.75"), Buck Vantage Pro, Kershaw Blur (assisted), Benchmade Mini-griptillian, Spyderco Native
$100 - Spyderco Military (4 inch blade), Benchmade Griptillian
There's a list of very popular knives at your price points. All are sturdy, one-handed opening knives with a pocket clip. Look them all up and see which one you like the most, because we aren't the ones who are going to put it in your pocket every day, you are. Higher price points generally mean better looks and better steel/handle material, at least in the list above. I can personally attest to the good quality of the Buck Vantage Pro, Kershaw Blur, and Kershaw Leek. I also have the Spyderco Endura but I haven't really gotten a chance to use it yet.