I have to carry a one-hand-opening knife because of physical limitations, and I do; but defense is what my gun is for, if worst comes to worst. The ones I use could be employed as weapons in a desperate last-ditch situation, like any knife, and could be deployed quickly. But I think the likelihood of my having to be involved in a knife fight is even less than the chances of my having to use my gun. That is to say, extremely unlikely. I carry knives to cut stuff.

Of the ones I carry one is over your price range, a Spyderco Endura. The other I use now is a Kershaw OSO Sweet assisted, similar to the Leek but with textured scales I can grip more easily. It's a liner lock, where the Leek is a frame lock. It's in the range you're looking at.

But another I would suggest is an assisted opener that I think is just a few bucks over $50. It's the SOG Flash II. It's substantial, reliable, and opens with a solid click. The drop point blade is just under four inches, legal in many jurisdictions. I gave mine to my nephew, but am considering replacing it.

I don't care at all for the American "tanto" point, which isn't much like any Japanese tanto I've seen. It's good for stabbing, less good for cutting. I quickly unloaded the only one I ever owned.

__________________
Oh well, what the hell.