I'll mirror what a lot of people have said here. One of my hobbies is purchasing cheap knives and then abusing them to the point of failure.
Overseas knives:
For ~$10 you really can't go wrong with a SRM knife. Particularly their rip off of the Sebenza.
I would say that the quality on that particular model at least is on par with anything that costs twice as much from Kershaw's
Chinese line. I'm not a big fan of the Enlan/Bee knives that some people recommend - the edges just don't hold up well. If you want
a big, beefy, gritty Benchmade-like knife check out the Ganzo knives.
Of course, the Opinel is a classic and an insane value, but unlikely to be chosen by a new knife buyer.
Condor: Fantastic value for the money, with a lifetime warranty - and surprisingly good CS from a South American manufacturer. Very tough blades that you may need to sharpen more often due to the 1075 that they use, but sharpen easily and feel like knives that easily cost twice as much.
Glock 78 - Great for throwing and digging. Just about indestructible. They won't hold an edge long, but they're cheap and double as a shovel.
US Companies:
Old Hickory 7" Butcher - No, seriously. You can sometimes find an older thick one on Ebay in good condition for about $10. Carbon steel, full tang, great heat treat. You could turn it into a project and grind the blade and handle down to a profile that you like and then oil up or even replace the scales.
Just about anything by CRKT. Especially Taiwanese made ones. They use cheap materials, but their QC and fit and finish for the price is impeccable. I used to work at a knife store and CRKT was about the only brand that you could take ten random samples from a batch of brand new knives and have them all function identically - same feeling in opening, same lock up... Like carbon copies... The blade steels used usually aren't the best, but they utilize them to their full potential.
Kershaw - you can find US made folders for <$30 that will have a lifetime warranty and just be great blades all around, but you have to shop around. Their Chinese knives have yet to impress me.
Spyderco - You could buy a Chinese Spydie or a used Seki for this price. Never a bad option.
Ka-Bar/Ontario - I lump these two companies together because basically... they're the same. Not owned by the same company. I know a lot of people feel strongly about one or the other - but in all honesty - I've abused similar knives from both brands for years and they've both performed identically. I almost wonder if it's the same factory churning out their 1095 and doing the heat treating because their blades in similar format knives seem to perform identically. I've heard stories of the occasional bad Ontario heat-treat, but out of the 20 or so I've tried to trash, not a single one has failed me yet, and I throw almost all of my fixed blades. If you shop around, you can get a decent US-made carbon steel knife that will most likely last you a lifetime if properly cared for.
That's all I can think of right now... I know there are more... Those were the brands that stuck out in my head.
Contrary to popular belief, a good knife CAN be had for under $30, but don't expect it perform the same as a $200 or so knife. To a certain extent, you get what you pay for, and after that it funnels down to supply and demand as well as hype (and unnecessary luxuries). I've seen $1000 custom knifes get trumped by $80 knives. Just do your research. There are a lot of knowledgeable individuals here.
Good luck!!!