IMHO: I see some of the Chinese brands were offered already, also mentioned some of the "US" sort of brands...
For $15-$20 I would stick with Ganzo 704 which is essentially copy of the H&K Benchmade.
I got 712, that is Bedlam's copy and I abuse it a lot, without much of a wear shown on the knife, steel is decent,
mechanism is just a good copy of proven design... In the pictures thread I posted a picture of this knife that I was using to cut a square hole in a 2X4 metal beam for a power outlet,
it did not show any wear after this...
An actual picture of my knife:
My first choice would be a US brand and someone already mentioned Thermite, which is excellent knife for the money, size wise and as design,
but here's what happens with the frame lock on the Thermite after few days only opening and closing the knife:
It's not a big deal, I guess, whoever knows how to fiddle with the knife would probably be able to fix such small things, otherwise I absolutely love the design of this Kershaw,
along with t he size.
Talking about size, the mentioned Zancudo is the same size as the small Rat - the second edition, they are both fine edc knifes, I also prefer the Zancudo but the truth is that they both are on the small side...
I personally would like a knife as the original Rat size.
If they had a larger size Zancudo I'd love to have one...
I heavily abused my small Rat and I have to say - it was a 0 (zero) play of the blade, impressive knife IMHO, along with the Zancudo, unfortunately I'm not happy with the sharpness retention of the Rat 2 but it could be my knife only, a bad batch or something, I don't know, my Zancudo is also made in Taiwan but if has excellent sharpness retention...
The only downsize of those both knifes that I can think about besides the size is the fact that it is effortless to close the blade if you hit it on the back, the liner lock does not hold at all, especially on the Zancudo, but they are not tactical knifes, when steady pressure is applied on the back of the blade they hold just fine...
If the OP shys away from Chinese productions ( I should say probably "brands") I'd say, go with the Kershaw Skyline - in my opinion - excellent design, good Sandvik steel and around $30-35 bucks...