I assume you have the standard 'kit' lens going down to 18mm at the short side?
Next, 'Wide Angle' or 'Ultra-Wide-Angle'?
One upon a time, when film cameras usually came with a fixed nonchargeable lens, the 'normal' angle of view was 'about' 45 degrees; aprox 50mm focal length on a 35mm film format. Any shorter was a wide-angle, and a 35mm focal length was the generic 'all-purpose' lens in most compact cameras, giving about 63Deg Angle-of-View. A 28mm focal length was a 'pretty' wide angle and gave a 75Deg AoV. Anything any much wider, tended to be a fish-eye lens.
If you have a kt 18-55, with the crop factor taken into account, this covers that entire range, offering 75deg is at the 18mm short end, and up.
These days, the crop factor stretching the cheap reach available from shorter lenses, has begged a new breed of short and wide focal lengths, where the crop factor compresses the 'wide' into the fishy region... which is significant.
A few folk of old may have gone as wide as perhaps 22 or even 20mm focal length, equivalent to about 14mm on a crop-camera, BUT, with such a short focal length they were often starting to get 'tricky' to use and showing some 'fishy' distortion at the edges, and modern UWA's suffer the same to worse, at short focal lengths and particularly closer subject ranges.... and I suspect for car advert type shots, this is the likely niggle.
I have both the Sigma 8-16 UWA, the 'estate agents favorite' and the Sigma 4.5 full round fish-eye, both for similar ish reasons.. usual subject motorbikes in shows or meets, where access is usually very tight, and the ability of an Ultra-Wide-Angle, to pack in an awful lot of the subject, from very close range, is almost the only way to get a photo of much more than just an engine or wheel or something...
BUT, Ultra-Wides are very tricky to work with, and to get those frame filling shots of say the side of a car, they really DO beg you back up and get some distance between camera and subject, to get a more flattering perspective. Working up close, its very hard to get it all in, and keep it natural, and very very small changes in the angle of incidence make very very big differences to the perspective of the picture.
The more common UWA is probably the Sigma 12-24, which is an AF lens, and has bee updated a coupe of times to offer a faster max aperture. OTMH its a little out of your budget, 'new' at around £250-£300, but you might snag one of the older versions in an offer, or grab one 2nd hand. The Tokina 11-16 is well regarded, and in the same price range.
BUT, its back to the camera-subject distance thing; IF you are working at such close ranges, you 'need' a UWA, then you will have to work a heck of a lot harder to make them 'work' for you.
If you back up, then you make life easy on yourself, and if you have the 18-55, you already have a wide-angle, and likely more than enough.
I would advise some caution diving into the wide-side, if you are new to SLR's, and only just bought an entry level camera.
Long zooms, deliver a lot of instant impact from cropping clutter out of the frame, and drawing the viewer's attention onto such a small portion of the scene.
Wides are the other way about. They pack a heck of a lot of scene into the frame, for you to worry about, and they shrink it all, so you have to be a heck of a lot more discerning ad pay attention to what you got, even before the perspective problem.
Advice of old; "North, South, East, West, check the corners then the rest!" When the ls packs more in the frame, there is more to demand you pay it attention ad work to frame to include interest and exclude distractions. Unlike long lenses, that simplify the image and almost deliver on demand impact, wides don't, they diminish impact and catch clutter, and beg you do so much more to make them work for you.
I'd say work with what you got; keep the pennies in the bank, until you know you can make it work for you.
It's a heck of a lot cheaper to shift a car to a bigger, and hopefully more picturesque location, to get some camera-subject distance, and get 'better' photos from the stage setting, than it is to expect a bit of glass to do it on the spot, in whatever space the cars plonked in.... and that's half the 'trick' of photography in general, looking to take control of whats in-front of the camera to get the best you can, not expecting to get it looking at the camera twiddling knobs ad dials and buttons and fiddling with all the stuff in the gadget bag you got out the catalog!
Finding other ways to skin the cat, and developing your craft, will I suspect do a lot more for you, than buying a fancy lens, straight off the batt and expecting it to do what you cannot. You will likely still decide you need a UWA, but hopefully, you'll have learned how to give yourself best chance with it, persevering with something a bit milder.
