70 - 200mm 2.8

[Danosborne6661]

Need a bit of advice photo peoples!
Looking at getting a 70-200mm 2.8 Lens but they really vary in price!

It's for a Nikon D90 body so I don't need things like the build in AF motor. For the price I'm looking at it won't have VR either. Basically they can really vary in prices. I'm looking at getting a Sigma/Tamron 70-200mm 2.8 but are these still good lenses? Let me know what the benefits are of spending £1000+ on one of these lenses over the £500 ones that I'm looking at off fleabay.

Thanks in advance