Dell Latitude 10, 3 versions

What are the differences between the three different dell latitude 10s that are offered on the website. I bought the $649 version and added the case to it and it came to 800 something all together but I want to know if the other versions have things like special features or extra addons. I already know the purpose of the more expensive versions but why in general do they cost more theres a $649 one, 750, and one around 900