Macro lenses are for extreme close-up shots - a few cm - most of us don't have them unless it's a particular field we're interested in.
A good wide angle to start with would be a 24mm or 28mm prime lens, or if you have more money to spend, a wide-angle zoom, say from 17-35mm-ish...
Depends really on how wide you think you 'need' to go...generally-speaking, the wider the lens, the more it'll cost due to the problems of making them distortion-free...
For car-photography in a studio, I'd go for a 24-70 f/2.8 or 28-70 f/2.8, but both are fairly pricey unless you buy second-hand.
Decide what you need and have a look through the 'For Sale' section here first. Usually there's a couple of wide-angles and wide-zooms lurking about...
I'd also say if you're serious about studio work, a future upgrade to your camera would be in order.
