If you want to keep it well under a hundred, get a Grip or Mini-Grip. One of the nicest things is you can get it with your choice of a hole or stud, and if you don't want to break your $100 budget on an S30V Ritter you can get a D2 Grip from Cabelas for $70.
That said, if you're willing to spend $100 I'd skip the Grips and go straight to the good stuff, the non-Zytel Axis locks. It's pretty much a matter of taste at that point. If you like Aluminum handles, the 940/941/943 are an incredible package in terms of being very light and thin in the pocket yet having a lot of cutting power. For heavy duty I'm a 730 fan, which these days means the 732. It's a freaking tank, and it fits my hand better than the 710, 805/6, or 520.
If "about $100" stretches to $120, basically the entire baseline Benchmade line is an option. For a sub-3" gent's knife I'm extremely fond of the 770 Grn/Blk, a limited edition in D2 steel and G10 instead of 154CM and carbon fibre or Aluminum - it cuts w-a-a-a-y out of its weight class. American Heritage Sports still had a couple at $120 when I got mine. For sheer cutting ability and the option of a sheeple friendly 2" slip joint blade when you want to be inconspicuous, the 921 is another lovely choice.
And a lot of people would say the 3" 705, which is being discontinued in favor of the 707, is the quintessential Axis lock - Benchmade's Delica, if you will. The biggest difference between them (very minor style changes aside) is the 705 is G10 over stainless liners, the 707 is aluminum. If you like Al, wait - if you don't, this is one to grab before it disappears.
