To stick in your price range, I'd go with a buck vantage pro. I've been extremely happy with mine. I'm an elementary PE teacher, but work at basspro as a second job selling guns. I open tons of boxes there. I'm constantly cutting open boxes to stock ammo, scent eliminators, rings etc...and open gun boxes for people. I also frequently have to cut through styrofoam after mounting a scope to get it to fit in the box. Cutting through styrofoam is a pretty great test of blade shape in relation to drag through a media. aus-8 blades on my sog's and cold steels lost an edge too quickly. Big, substantial blades like my contego were too thick and had too much drag through carboard and styrofoam. My contego will hold an edge forever, but it's blade geometry doesn't lend itself well to slicing through boxes and styrofoam.
My vantage pro is pretty amazing at retail work. It's a pretty thin blade with little drag with properly (bos) heat treated s30v steel. The lock was properly timed out of the box(slightly early, after break-in is timed on the early side, but right where it should be). The blade was centered perfect. My only complaints about the knife come from the fit of the cnc'd g10 to the liners. The handle slabs are overcut and need fitting. After profiling them to round them out, the knife became much, much more ergonomic. Rounding out the g10 slabs also enhanced the usefulness of the pretty small flipper. Some either grind out the thumb hole in the blade to make a wave, or loop a zip-tie to make a redneck wave. I haven't found either necessary and just use the flipper when I need it.
After a couple years of use, the lockup is still rock solid. For about $70, it's hard to beat for your uses.
http://www.knifecenter.com/item/BU3...o-Large-Linerlock-Folder-3-14-inch-S30V-Blade