I had the same mindset as you initially, wanting to spend as little on lenses as possible. What I have realised after owning a DLSR for a while now, is that the more you invest in quality lenses, the better.
I have a D40X and I bought the Sigma 70-300mm DG Macro lens. It didn't autofocus, but that wasn't really a great concern for me as I have practiced a lot with manual focus and I think I can probably do it as quickly and possibly more accurately than the lens itself anyway! I used this lens for a while, and enjoyed it, but then upgraded to the 70-300mm Nikon VR lens which I found far superior in quality. It made me realise that had I have saved my money and not spent it on the Sigma lens just because it had the benefit of being cheaper, then I would have been better off.