Sorry; I've stated myself poorly.
I hold four kenpo karate belts, study Brazilian and kali knife fighting, am proficient in the use of various types of firearms and am in excellent physical condition. If necessary, I believe I can use a knife to some degree of effectiveness for personal defense.
However, I have very little knowledge as to WHICH knife is best suited for the size, price range, quality and brand that I need. That's why I'm consulting with Those Who Know.
Again, I'm in need of a decent quality tac folder with belt clip which is not in the $100-$200 stratosphere and has a blade length of 5-6 inches. This knife will be carried primarily when I cannot pack a handgun. My current "carry" knives are the Walther Allied Forces tac folder, which is an excellent, razor sharp knife but seems a bit heavy and has a shorter blade than I'd prefer... the Smith and Wesson HRT boot knife... and the Walther P99 Tactical knife. Yes, I'm a Walther fan, and yes, I know they don't make their own knives.

I normally spend $15-$50 on a knife, and that quality range seems suitable for my purposes.
I don't mind searching on my own, but if you know of a web site that carries the specific knife you recommend, please list it. Thank you all again for your advice.