Upload & Sell: Off
Why not get a second hand Sigma 10-20mm? They are only about $350-$400, that price is likely the lowest you are going to pay for a lens that is going to have many desirable features as the most expensive alternative, bar the superior image quality they produce.
I've recently moved to full frame and shoot with a 17-40mm and prior to that the 10-Sigma 20mm and 17-70mm were my most used combo for travel and wide. The 17-70mm was a great walk around, nice and sharp, low f/ at wider angles and a good size and weight. The 10-20mm WIDE but but produces great results for a lens at market price.
I'm planning on selling these two lenses in the coming weeks either on the forum or on ebay if you are interested.
If the Siggies are too expensive you could look at the antique/vintage lens market and get manual focus lenses. You would have to shop around and do some research but that could be worthwhile.