Thanks again for all your comments, much appreciated.
Well, I finally got one! In fact I ended up with a D300s off Ebay for £500. It has over 41,000 shutter actuations (well over my concern for 30,000). I probably wouldn't have bothered if it wasn't for your feedback.
Anyway, it came yesterday and it's in very good condition. Hardly a mark on it. Everything seems to function ok (though I'm still getting used to it). The only thing that doesn't seem right is the wheel in front of the shutter button (forgot what you call it) doesn't spin and click as nicely as the rear one. This might be how it should be, I don't know.