How wide is wide, and is fish-eye desired?
If you want something lowbuck but still capable of quality photos and don't mind manual settings, you can get a Zenitar 16mm fisheye from eBay - it doesn't normally come in a Canon mount but several sellers will sell you the Pentax M42 mount with an adapter to allow it to work on an EOS mount. Assuming that there are no issues with the adapter (I honestly don't know), the lens itself is a lot of fun and relatively very cheap, probably under $150 for everything. The fisheye effect isn't very pronounced on a DSLR which is good or bad depending on what you're after. If you don't want fisheye, the photos can be "straightened" fairly easily by a variety of software.
It is 100% manual so you'll need to meter by hand, to saw nothing of focusing, but it's wide enough that you can usually just leave it on infinity and it'll be in focus. The other lenses can probably produce slightly superior photos and certainly are much easier to use, but you'll probably have to pay 3-5x as much. It's a great bang-for-the-buck lens.