Digital photography

might sound like a stupid question, but what's the least you can spend on a set up to get shots like this:

http://4.bp.blogspot.com/-KrQhujKWpg0/TjGow5q1FlI/AAAAAAAAN_U/5OjIeoKsQMY/s320/downhill%2Bmountain%2Bbiking%2Bwallpapers-2.jpg

if I had a 4 grand set up would it be easy to get a clear image with nice bokeh etc.

Yes, because you need a fast lens. Possibly a zoom and they contain a huge amount of expensive glass. Like the big ones you see sports photogs with.

also, anyone got any advice about the standard settings for this sort of shot, assuming there's enough natural light to not need a flash. ISO, shutter speed etc.?

In bright light like that photo you could shoot 1/1000 at f5 iso160, but your zoom length will cut down the depth of field and base aperture. You should 'zone focus' as others have said. Manually focussing at the point you want to take the photograph and wait for the rider to reach that point then shoot 5 or 6 frames as fast as possible. If your body has aperture preview you can check the zone of focus on the ground or nearby post etc.

If it were me I'd try with a fast 135 prime on a full frame body, probably get 1 in 100 decent photos though! As money's an issue try an f2 50mm manual focus and crop them or get closer to the subject if possible.