Jack,
By that logic, would you carry a Lorcin?
Yeah, you might get a shot of two out of it, but maybe you won't.
As the price point goes up, you're going to notice some things change.
Steel.
there's a difference between the steel used in a $10 knife and a $100 knife. The difference between a $50 and a $100 may not be as appreciable. I like the ATS-55/34 or CPM440-V, but I don't think the object being cut will know the difference. Edge holding, corrosion resistance, and ability to sharpen well should be factors. You don't want something to sit in your pocket and have it rust out (especially if you live in a humid/tropical area where the air is salty.)
Handle materials.
You can either go with a Zytel/Fiberglas Reinfornced Nylon(FRN), G10, Carbon Fiber, wood, stainless, titanium... etc...etc.
I have no problem with Zytel, and it will certainly lower the price of your knife. I find stainless and carbon fiber to be a little too slippery. You also have to consider that the conditions this knife will be used in may not be optimal for keeping a good grip (wet from rain/blood, etc)
LOCKUP
Your defense knife should have a good, solid, lockup. You don't want vertical or horizontal play, and you don't want to be able to cause the lock to fail by either squeezing the handle hard (white knuckle test) or by slamming the spine of the blade on a table (for liner locks) Dealing with folders means dealing with moving parts, which is just bound to bring Mr. Murphy into the equation. This is the best reason to justify a more expensive knife.
I would echo the suggestion of some others and recommend the Spyderco Endura. If you have smaller hands, try the Spyderco Delica. Both have FRN handles, ATS-55 Steel, and lock back devices. You should be able to find one on the net for $45
If you want to go up a step from there, try the Benchmade AFCK ($85).. If you want to go up another step, there's the BM 710 ($100) (Axis Lock) or something from Round Eye Knife and Tool (REKAT ~ $120-$150)
Whatever you get, practice, practice, practice. Especially drawing the blade quickly. Always carry it in the same pocket, and don't put change in that pocket (can get stuck in the knife, DOH!)
http://www.combattech.com/ has some good training stuff, and is as good a place to start as any other.
good luck, and let us know what you decide to go with.
Tom
[This message has been edited by TomMarker (edited July 18, 2000).]