You really can't go wrong with either Canon or Nikon. I shoot a 7D and usually have my Tokina 12-24 or Canon 24-70 for car shows. The Tokina is nice & wide, so I can get fairly close to the car & get it all in the frame, it also makes it easier to get the typical 3/4 shot with cars parked next to each other and not get the neighboring car. Get really close & play with perspective distortion. Some examples (mostly shot with the mentioned lenses & either the 7D or my old 20D): Automotive - Chris Laudermilk Photography
The main thing is to spend your money on the best lens you can. Bodies come & go, and anything from the last few years is more than capable enough--good lenses will stay with you.
Take a look at KEH.com. They are one of the biggest used camera outfits & are super conservative on their condition ratings. I have no problem looking at stuff they rate as "Bargain"--I got a Mamiya 645 rig all at that rating & it just had some scuffs & needed a little cosmetic cleanup (no surprise on a 20-year-old rig that probably saw constant pro use for years); it works flawlessly.