Also, if you're going to buy the M17x, then you need to make sure that you are buying it in a configuration that includes the upgraded 1920x1080 display. You generally should not buy the Alienware M17x in any configuration that includes the default 1600x900 display.
1600x900 resolution in a 17.3" display makes things onscreen large, and 17.3" displays that have 1600x900 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 (15.6" 1366x768, 17.3" 1600x900, etc.) when it is reasonable to do so, unless you require the larger text for eyesight-related reasons.
This puts the cheapest recommendable configuration of the M17x at $1649, and then the GPU upgrades will add further cost onto that.