It’s hard to go wrong with the RSK for a little over $100. I have a bunch of Benchmades, and like them a lot. The Axis lock is very easy to use, and deploy the knife one-handed. The CPM-S30V steel is quite good.
I have a Kershaw Blur - it is spring assisted. It’s a decent little knife for the money.
Do you want or care about serrations on the blade? Personally, I am not a fan.
For around $100-$150, Emerson and Spyderco also make very good knives. Emerson has a Waved opener, which allows you to deploy the knife with one hand. Earnie licensed the Wave to Sal, and Spyderco uses it with the permission of Emerson.
Is self-defense a consideration, as you stated? I am a fan of carrying my knife on the left side, and being able to deploy it with a single hand. An Emerson Mini-Commander is pretty handy that way. You can deploy it by simply pulling it from your pocket.
This is the non-serrated one that keeps finding it’s way back into my pocket as my EDC:
http://www.emersonknives.com/ekMiniCQC7BW.php
The Wave is awesome. It’s good for weapon retention that way. If need be, you can cut someone’s hand off your weapon during a disarm attempt in a fast and efficient manner.
BTW, Earnie will drill one of his right-handed knives for left-handed carry. I think he charged me $17 for it.
May I suggest a vendor to buy a knife from? Grant at G&R Tactical sells Benchmades. If he does not carry what you need, New Graham Pharmacy is a family business, selling knives for a long time. They have great service. Mike and Annie remind me a lot of Grant and Roxanne. Highly knowledgable, and customer-focused.
Also, something to think about on the Spyderco knives. Sal sells trainers, or “drones”, for some of his live blades. So for about $130, you can get a carry knife and a trainer.
http://www.spyderco.com/catalog/details.php?product=227
http://www.spyderco.com/catalog/details.php?product=251
You would never buy a pistol, and not get training for it. So why would you would ever buy a knife and forget to train with it?
I’ll be happy to help with further info if you wish. Stay safe, and good luck.