How much you spend really depends on your monitor. The better calibration tools rely on being able to adjust monitor settings in what they call pre-calibration. To do this you need to be able to set the colour temperature, and adjust contrast, brightness and the RGB settings individually.
If you can't do that and only have fixed colour temp settings then to be honest you may as well go for a cheaper calibration tool as you won't be able to use many of the features of the more expensive models. It's much better to be able to use pre-cal to adjust your monitor as that means the software won't have to mess around quite so much with your video card settings and it's LUT.
My monitor falls into this category so I went for the ColorPlus cheap and cheerful. It works perfectly well for me!!
If you want to edit pictures and want them to stand a chance of looking either half decent on someone else's PC, or want to get close to an accurate print, you simply MUST use a hardware calibration tool.