Another vote for the mini-Griptilian. It's not quite under $50, unless you look here on the exchange forums, but it's also not much more than $50.
It's a solid knife despite the FRN handles, has the Axis lock (and mine was buttery smooth out of the box), two great blade styles to choose from, up to at least 4 different handle colors to choose from (black, green, blue, yellow), and, while small, still fills the hand better than most 3" knives.
It's a great knife!
Matthew