For quite some time now it has been the best laptop in it's price range, only feature that is missing is a higher resolution screen. But that is still standard at this price range.
Sometimes the 1920x1080 one gets a good sale going on, and brings it within $100 of the standard version. You may wish to wait for this. It also has a Blu-Ray reader for the upgraded version.
First, if you are looking at buying the Lenovo IdeaPad Y580, you need to make sure that the model you are buying comes with the 1920x1080 display and not the 1366x768 display.
1366x768 resolution in a 15.6 inch display make things onscreen large, and 15.6 inch displays that have 1366x768 resolution tend to be low-grade LCD panels with very poor image quality due to low contrast. You should make a point to avoid displays like this when it is reasonable to do so, unless you require the larger text for eyesight related reasons. 15.6" 1920x1080 displays are generally great, but the reason you need to be looking at laptops that come with 15.6" 1920x1080 displays instead of 15.6" 1366x768 displays isn't just because of how good the 1920x1080 displays are, it's also because of how bad the 1366x768 displays are.
This is more of an issue than the other differences between various models of the Y580 as well as other laptops. A GT 650M (as opposed to the Y580's GTX 660M) is not a terrible GPU, an i5-3210M (as opposed to the Y580's i7-3630QM) is not a terrible processor, but a 15.6" 1366x768 display is a terrible display. You should be concerned with improving a display that's pretty bad before you start trying to improve upon performance that's already pretty good. If a 1920x1080-model Y580 fits in your budget, then great. But if it doesn't, then a 1366x768-model Y580 is not an alternative nor a good choice; look at other laptops.
Here's a general-case up-to-date purchase guide for the Y580: