Help about the Sigma 30mm 1.4 lens?

So I really want to buy the sigma lens, but buying it new is way too pricey for me so I'm looking on eBay. I'm confused though that there are different versions of the sigma lens. For ex: DC vs DG and lens made for NIKON or Canon or Sigma.

I have a canon t3i and I'm trying to figure out what versions of the sigma lens will work.

Please help.

Added (1). the one I'm really wondering about is called: SIGMA 30mm F1.4 EX DC HSM For SIGMA AF +++NEAR MINT in BOX+++From JAPAN #258

would this work for the canon t3i, or just for Sigma cameras?

You want a lens to tell you it is Canon mount. That one will not fit your camera

Always make sure that any lens you buy is made specifically for your Canon camera. In the case of the T3i/600D, you need to make sure that the lenses you buy are EF-S or EF mount lenses.

If you do not have an abundance of money, the first step before buying something is being able to enunciate what you will be using it for. Can you do that?