I agree with suggestions for both third party lenses
Tokina 11-16 and Sigma 10-20. I have both the Sigma and Canon 10-22. Call it luck of the "bad/good copy" whatever...I shoot with my Sigma more often than Canon (I like it better

...And as far as getting a bad copy, Sigma's customer service and warranties are phenomenal. They'll make sure you get an excellent copy...as long as it's within the 3 year warranty period
As far a "budget" WA lens...it's tough to buy "new" under $400. However, there is a very active used/pre-owned market (I say pre-owned because I know several folks that have invested in DSLR gear...bodies, lenses, flash, filters, etc....ONLY to leave it at home and take the P&S with them). The third party lenses don't seem to hold their value as well, so you can find them for 25-30% off retail. Look for the right seller, locally on Craigslist. Spend some time looking and I'd bet you'll find that same character I'm talking about...More money than sense and ready to take the loss to recoup some of their lost "DSLR" investment
While the 15-xx and 17-xx and 18-xx are actual wide angles...on a crop sensor, they're not going to give you much better than 24-whatever up to 29/30-whatever.
Slipping into the 10-22, 10-20, 11-16, you'll be able to achieve a more ultra wide angle shot with wide angle capability (16-32 on the Sigma)...
Again, tough to find them at a budget price and if you spend budget money on a new lens, you'll find lesser build quality, slower AF, aperture handicap, more CA and distortion at either end (wide or tele), and overall...a lesser quality lens, IMO. After 20 years of shooting, I've come to the realization that a true wide angle lens should be just that...when you try to mix both in a zoom with more than 3x zoom, there are trade offs at one end or the other...or BOTH!
Good Luck and I agreee....save your money til your ready to buy the right lens for you. Check out this site
http://www.lensrentals.com/category/wide-angle/for-all for the chance to rent all of these lenses...without insurance, $41 a week, with insurance, $48 a week (give or take a buck or two).
J