I'm afraid that a shutter replacement - that's what this almost certainly is - usually runs about $450, and for some reason that doesn't seem to depend much on which camera is involved. The D7k does not clear twice as fast. I think your best bet is a used D300. I think you'll find that it is rather better suited to your needs than a D7k, in terms of frame rate, control system, and AF performance. Low light performance is at least as good. Don't let the fact that it is "older" or "obsolete" obscure the fact that it is a top-line machine.
One of my friends is a working pro that shoots a D300 interchangeably with a D3 - and he does motorsports. He routinely shoots very long sequences.
_____ Brian... a bicoastal Nikonian and Team Member
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