The term 1k or any number w/ a "k" in it started way back from online games. The "k" is a short replacement for "thousand". For some instances , if you double the use of "k" in a number like "1kk" , it means raise the default value by a thousand which is 1 million (or 1M) in short.
Player A : I am selling a *random rare item* , also a *random rare weapon* pm me if interested.
Player B : how much is one for the item ?
Player A : 1k each.
Player B : How bout the weapon ?
Player : 1kk (or 1M); negotiable.