I'm on the market for an autofocus telephoto lens for my D3000. I want it for automotive applications—particularly trackside photography. Now, I know there's a strong Jalop presence on this subforum so I ask: is 200mm or 210 long enough, or I should I aim for a 300mm?

Ideally I'd get the AF-S 70-300mm f/4.5-5.6 VR but I'm not looking to spend that much. Is there a cheaper way to AF and 300mm or is 210mm ample or am I stuck between two rocks and three hard places?