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Yes, you will find that, depending on the focal length and aperture, that Nikon lenses can be extremely expensive. The Sigma and Tamron equivalents are almost always cheaper. The main difference you'll see is the aperture at 200mm. For example, the Nikon is 5.6 @ 200mm where the Sigma and Tamron are 6.3. The other difference is the quality of the vibration reduction. Better VR can be very useful in handheld situations. Will you notice the difference? Maybe, but that depends on your experience and what you are ultimately looking to achieve.
I assume you want a lens with this much diversity because you want something that is portable and don't want to change lenses often? The alternative, besides getting a Sigma or Tamron is sticking with your kit lens and getting the Nikon 55-200mm or 55-300mm, which is much cheaper. I have both but I prefer the 55-300.