Kershaw Thermite and the Kershaw Injection (3.5) are on the top of my list of knives that have absolutely impressed the crap out of me for ~$30 knives.
Probably the only thing that comes close (IMO) is the Tenacious series from Spyderco. I tend to try and get as much quality, fit/finish, upgraded materials, and overall beefiness/reliability under what I consider hard-use when I determine something as high-value for a budget knife.
There are lots of nice perfectly good folders in the budget category, but very few that I consider to be truly "high value" folders in that category.