How to add cost function to an object in .mat file ?

I have a coordinates of a polygon in 2D form, i.e., x and y coordinates of a polygon, now i want to add cost to that polygon, can you tell me how to add cost to that polygon with x, y coordinates.

Ex: Suppose the coordinates of the polygon are [12.45 36.05 ; 12.45 35.7; 12.9 35.65; 12.9 36; 12.7 36; 12.7 36.1; 12.4 36.05] now i want to add 1000 as cost of the polygon. How can i add? please reply.