Does a lens converter affect the image quality?

I want to get a wide angle lens and it's $180 cheaper to get the nikon over the canon. Is there a good reason not to use a nikon lens with an adaptor over a canon lens? I would get the canon but I need it in less than a week for a holiday and I just can't find a good deal for the canon anywhere!

If you use such a mount converter, you often won't get full functionality from the lens in terms of aperture control and auto focusing not functioning. You may net even get the metering to work, and because the lens to sensor gap will be different the effective focal length may be changed. Finally, if your camera performs any "lens correction" then it can't do this with a lens it does not know.

Have you considered getting a third party Canon mount lens from the likes of Sigma, Tokina, or Tamron lens?

Are you referring to a converter or an adapter? The latter term is usually reserved for a mechanism used to use lenses of one brand to be mounted on the camera body of another brand, say a nikon lens on a canon body. A converter usually means an attachment (actually a lens) that can be screwed onto the existing lens in much the same way as a filter, to give it a wide-angle of tele effect. The exceptions are the original tele-converters (same term, totally different device) from Canon and Nikon, which are mounted between the camera body and the lens and double the tele-zoom reach of the original lens; these high-quality converters can cost several hundreds of $$$.
Btw, Canon and Nikon both offer a vast range of lenses, and since they're immediate competitors, their prices for comparable products would never differ for more than a few per cent.

To be blunt: screw-on converters are complete rubbish, a poor man's solution that gives very disappointing results like soft, unsharp images with lots of colour shifting and distortion. They're sold by the thousands on Ebay, and are advertised as having been specifically made for Canon, Nikon, Pentax, etc. But are in fact, one and the same piece of junk. For instance, if you'd buy a converter advertised specifically for Nikon, you'd get exactly the same converter as you would've got had you ordered a Canon model.

Real wide-angle lens (as opposed to converters) can be very expensive, depending on lens speed and quality, but a good, original Nikon 18 - 55 mm wide-to-medium-tele zoom for DX-sensor cameras costs as little as $ 107 on adarama.com, giving you a wide-angle view roughly equivalent to a 28 mm wide-angle on a classic film camera. As someone else has already answered: good and less expensive alterrnatives would be Tamron, Sigma and Tokina lenses, especially when you want to go wider than 18 mm, where things start to get substantially more expensive.

If what you're referring to is a Nikon to Canon mount converter that attaches to the back of the lens, I'd definitely NOT do it. The lens will not be able to auto-focus or communicate with the camera body. If it's a Nikon G lens, chances are it won't have an external f-stop ring, and therefore you wouldn't be able to change the aperture at all. If it does have an external f-stop ring, the picture will dim noticeably as you manually close down the aperture. At the high f-stops you may not see anything through your viewfinder at all.

If the lens in question is a manual Nikon AIS lens that could be gotten inexpensively, I'd say it could be worth it. But be aware of the drawbacks…