Okay, so first, just as with knives, it comes down to what you need it to do. How much you need to spend really depends on what you're trying to get out of it. With knives, I tend to think cost comes down to fit and finish and features that are relatively insignificant when it comes to the end goal--cutting stuff.
However, as the knives get bigger, things get more interesting. The demands placed upon a sword are substantially different than the demands placed on a knife. You don't see many pictures of a 3" blade breaking in half, even with cheap gas station specials. The amount of force required for such is quite different, and harmonics have a negligible effect on a shorter blade. Similarly, a short blade is substantially more forgiving of any flaws in the grinding. With a longer blade (say, over a foot OAL), you're pretty much guaranteed to end up with at least a little warp post heat treat, unless it's been precision ground, say, via CNC or something. So, the stresses you face are quite different, which is why swords need to have a lot more attention paid to things like cross-section, geometry, edge geometry, shearing, etc. The stresses that a sword faces are not at all the same kind of stresses faced by a small knife, and we're talking macro scale here, not anything tiny.
That's why you can have videos of a guy smacking a cheap Chinese sword on a table and have the end break off and stab into him. Because of the length, a force that would barely be noticed by a small knife can be catastrophic in a sword. The physics are rather more interesting with longer blades. For instance, take a yard stick and flex it. You'll notice you can probably bend or break it very easily if you grasp at the end. In contrast, try using the same amount of force, but grasp only a few inches apart. The difference should be pretty evident.
Too, working swords often have more expected of them than EDC knives. They need to be able to withstand severe and repeated impacts (such as a sword into armor, or bodies, etc--duplicated by hard bamboo wrapped in tatami), and thus need to be flexible enough to take the shock and return to true. They need to be able to withstand impacts on the point. They need to stay razor sharp through hundreds of cuts and impacts on a wide variety of substances as well. If your sword were to dull during combat, for instance, that could cost you your life. Not that combat is even a remote likelihood for a sword these days, but still, the point holds true. I suppose, if I were to make an analogy, it would be regarding throwing knives. Those face sharp impacts and much more rotational force than your average knife, and if you throw a knife designed for cutting on a regular basis, you can be assured that it will eventually break. Swords must face those same impacts, and still be able to cut. The heat treat requires much more nuance (or you have to use a more capable steel, where with a knife, steel is really just a novelty). For instance, you will be hard pressed to find a 440 steel sword that won't break under use. Sword steels must be very tough, and yet still retain a balance so that the edge will remain functional. You talk of edge-rolling or chipping as though they're just a possibility. If the sword isn't done just right, that kind of damage is extremely likely upon impact on a harder target, or even an easier target that you've struck at the wrong angle.
And then, the geometry and balance is significantly more important for a sword than for a short knife. Consider katana. Your average cheap katana is just slightly bent along a curve. It takes the rough form, enough to fool the untrained eye, but the angles aren't quite right. A sword designed for cuts will take into account the way your arms and body move to keep the blade at precisely the right angle to maximize force and cutting ability through the entire length of the blade and the cut. That's why, if you look at pictures of a really well-done sword (such as Dan Keffeler's Super Assassin wakizashi, for instance, or a genuine nihonto), you'll see the hilt of the sword is actually often at an angle to the blade. And yet, in a cheap blade, you won't see the same attention to design, and consequently, an experienced cutter will notice a distinct and significant difference in cutting ability.
The list goes on. Swords are not just large knives, and even if they were, the massive size differential would still mean that something that wouldn't impact performance on a knife can result in a broken blade for a sword.
