There is no way to get coordinate positions of your target or anyone else. The only way is for other players that are using addons to send that data to one another from their respective GetPlayerMapPosition calls.
You can only guess at ranges based on whether certain spells/abilities are in range.
Another example would be the range displays in Stuf unit frames. (0-5yards, 5-10, etc)
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh