I am looking for a telephoto lens for my Nikon D5000 to use for shooting wildlife on an upcoming trip. My research has shown I need a 70-300 mm, however, I'm a novice photographer and don't want to spend more than $300-400 for the lens (it can be refurbished). I saw a Nikon lens with image stabilization, however, I can't seem to find it anywhere to buy it. Are there other brands -- Sigma for example -- that you can recommend and, of so, which lens. I read a review of a Sigma lens and it said it was slow on auto focus. I may not have much time to focus if my subject is moving so I want the best that my small budget can afford.