I want to pick up a 20mm lens for my Canon Eos elan7e but even the used Canon lenses are a bit out of my price range. I was browsing the used inventory at KEH and they have some sigma lenses that are in my price range. Does anyone have any experience with this brand? How do they compare with Canon? Are there any other brands that I should look into? Also, can anyone recommend a good online store for lenses and other accessories? Thanks for your help.