Hi
I've just been down this road, trying to weigh up cost vs features and lenses.
It started off with a workmate tempting me with his Canon 400D complete with a couple of lenses (18-55 and 55-250 IIRC)
Anyway, after much hunting around and reading up on specs and reviews, I eventually found myself going for a 550D with the standard 18-55mm kit lens - this was second hand but in as-new condition and all for just £300 (which seemed a reasonable price to me). I also bought a 17-85mm lens to use in place of the standard 18-55 (this was another £150 and again in as new condition).
My choice in camera was driven mainly by the processor, with the 550D having the DIGIC4 which is much better than the DIGIC3 (450D) and better still than the DIGIC2 (400D). The 550D is pretty much the same camera as the current model (the 600D) but without the flip out screen - and I couldn't justify the price premium just for that feature. The DIGIC4 has much better low light handling than the DIGIC3 and it was introduced from the Canon EOS 500D - as such, if you want Canon, I would recommend looking for a 500D or better.
Lenses are a different matter - if you're wanting to photograph stock cars, then I guess you're going to be a bit of a distance away from them and may need a relatively good telephoto lens - probably one with image stabilisation, unless you want to invest in a tripod too. And it's the lenses where things start to get really expensive. Here, you can pay anything from £50 to £5000 depending on your budget, needs and wants. It's hard to recommend here as it's purely down to personal preference. You could argue that you would do fine with an entry level 70-300 mm lens, but then again, if you read reviews and the technical details in the images interest you, you may be better off with a 300mm prime lens at around £1200 (2nd hand).
At the price I paid, I think I got a relative bargain - keep shopping around and there are bargains out there to be had.