How much do i pay for over limit of checked luggage?

It vary depend with the carrier that you've chosen, with point of you journey Starts and Ends and with class of your travel (Economy, Business, First etc.) as well.

If it is only with 1-2 Kg extra they may allow you. (Sometimes May NOT) but if it is weighing more you have to pay carrier decided Extra Baggage allowances according to your originating and destination points.