Hi there gazamc!
Some alternatives that you can consider:
Nikon 70-300 ED
Tamron 70 - 300
I had researched on the net for these 3 lens, and I just recently bought the Nikon variant, because the pricing difference between these 3 lens is not that siginficant, and comments made say that the Nikon variant is slightly sharper.
And it's partly because it's a Nikon. I'm quite a sucker for nikon lenses.
Build quality is rather OK, although not up to standard to the more expensive lens like the 80-200 f2.8 types.
It's rather sharp and comparable to the 80-200 f2.8, but only if you don't use it wide open (ie, at apertures from f8 - f11), at focal ranges from 70-200. At 300mm, there is slight softness at all apertures.
Read more about this lens @ the Nikonians website.
www.nikonians.org
If you have friends in HK, you can ask them to get it for you @ this shop called Wing Shing for HKD$1980 (approx $450). Last time I checked, Cathay is selling this at $588 w/o GST.
There are reportedly rumors about the Tamron lens being the same as the Nikon variant, but I'm not really that sure on the extent of that rumor...
Just a sample image for you...
http://web.singnet.com.sg/~choonkng/sample.jpg (warning: full file size @ 72ppi). Image is slightly compressed to conserve file size. The original 2.6MB image is slightly sharper than this.
ISO 400:: 1/800s @ f8 @ 70mm (equivalent to 105mm on 35mm). Taken with a D100.
If you're working on a shoestring budget, get the 70-300G lens. Build quality is poorer, but hey, it's quite good as well!
Hope my comments helped...