If a non-knife person asks me for a budget recommendation under $20 I usually suggest the Oso. It's inexpensive, good quality for the money, attractive and light weight, with a mid-sized 3" blade made out of decent budget stainless steel. Easy to sharpen, has a fast assisted opening ("snicks" open like a little knife who thinks it's a big knife), good lock up, no play in my blade, decent grip for GFN, with a comfortable handle and a very useful blade shape for slicing and the light use most "non knife" folks will use it for. My copy is not as centered as it was when I first got it, but I suspect tightening the pivot screw would might fix that, I just haven't gotten around to it.
With 3" of blade it's right in that sweet spot if you want a knife big enough to get a grip on but not overly large. Mostly, it's a very easy knife to wear with rounded handle edges and no thumb studs. I have to wear slacks at work even though I do manual labor that requires a knife, and it wears well clipped into my pocket without scratching up my hands when I reach in for other items. No sharp edges on the pocket clip either. And it's fairly good looking to boot.
A true knife guy or gal without need of another budget knife, or someone with big hands, may want to skip the Oso. Ken Onion has designed so many nicer knives for not that much more money. Plus, it's not half the work knife something like an Ontario Rat I or II is for around $28, but I don't think you'll find much better for $18. I've seen it as low as $12 on sale various places, but $18-$20 seems to be the going rate. And holding out to save a few bucks makes no sense to me unless you enjoy the budget hunt for what it is, as I am ashamed to admit I do.
Something to watch out for while opening the Oso (any knife really) is letting the heel of your palm cover the very bottom of the knife while triggering the assisted opening. The point is sharp, and common sense says don't let your hand cover that very bottom as it flicks open, but I've done it myself, lol. Luckily no blood.