I know about DSLR’s in the capacity that I’m a serious but amateur photgrapher, but I’ve never really tried motorsports photography properly yet.
*shameless promotion*
http://www.flickr.com/photos/newnhamlea1/
But something like the canon 1100d or the older 1000d would be a good starting point, maybe buy the 55-250mm lens shortly afterwards too, that would be good for motorsports.
oh and as for prices, look at this website,
http://www.camerapricebuster.co.uk/
it helped me get a good deal on my 550d a while back.