Here's how the process of replacing the screen would go if you did it yourself, or paid someone to do it. Buy the glass (between $45-$60 USD) then use a heat gun to loosen the current glass being super careful not to overheat and destroy anything inside. There's about an 80% chance you'll damage the wifi antenna so go ahead and order that too ($5). It's because the antenna is glued to the glass and body, it takes a really steady and experienced hand to do this without damaging the antenna... Next you remove the battery and motherboard and unplug the digitizer(glass) and plug in the new one and reassemble... It will take you a few hours to do if you haven't done it before..
Where i'm at, there are shops advertising repair services, but they'll charge you $200 USD(minimum) to repair it.
If you want to do this yourself order the parts on amazon.com or ebay, use ifixit.com for the guide, but as someone who has done this many times.. i don't recommend it for a small crack like you described.. I'd sell it to a family member or friend who won't mind a slight discount due to the defect.
Given the difficulty of repair, you'll be ripped off by any company attempting to buy it from you, stick with ebay or craigslist.