Having a really sharp knife available in the kitchen cuts down on your prep time and therefore makes your cooking experience much more pleasant.
But great kitchen knives cost a bundle, right?
According to this video by Kohaku the cat's personal chef Jun Yoshizuki of Jun's Kitchen (previously at Neatorama) you don't have to spend that much on a quality kitchen knife- you just have to sharpen it right:
So I got a lot of requests to make a video about knives and, like, asked me for my recommendations and stuff. But what I can recommend you is going to depend on your budget, what shapes you want your knives to be, which steel you want your knives to be made of, brand, design, there’s just so many things that you need to think about before getting one. But one thing I can say for sure is that, no matter how much you’re going to spend on your knives, they eventually get dull, and you need to sharpen them.
-Via Laughing Squid
Regardless, the knives I've seen at dollar stores had such huge gouges in the blade, you would spend a lot of time or need power tools to sharpen it. A couple of them also had such horrible handles that you could cut yourself on the metal protruding from the badly cast plastic handles.
You don't need to spend a lot on a knife, as you can get some cheap ones at a restaurant supplier that might not be pretty, but will be easier to sharpen and stay sharp longer. Used knives can be cheap and easy to sharpen as long as they aren't dinged up. But that is a long ways from saying the cheapest knives are good enough just because they can be sharpened.