I think for folks that buy throw-away knives it's probably not worth it to spend more that $20-30 on a sharpener if at all. But if you've been buying (or receiving) knives for decades, receiving them from father / grandfather, or own any of considerable value, then it makes perfect sense to get a good sharpening system. The idea of sharpening is simple, but what the expensive setups do is maintain the perfect angle throughout the sharpening process, and some flip the knife over (or get you access to the other side) within a split second or in real-time (like for the wicked edge), and these systems usually have a collection of quality stones and some setups easily handle different lengths of blades. After checking out a lot of systems and taking a while to eventually to commit to it, I eventually opted for a Hapstone setup. They come in a variety of configurations at different price points. If I didn't get it, I think I would have gotten the KME. Some guys like the TSPROF setup which is similar to the Hapstone. Another important detail to watch for is the clamp(s) that hold the blade so it doesn't get in the way of getting the angle you want. If you were on a tight budget but still wanted a solid, compact setup with quality stones, check out the KME.
EDIT: I should mention that the Hapstone system, which is completely modular and allows for many changes and upgrades, also has an option for blade support that is magnetic so you don't have to worry about the stone contacting the clamp.