I need too know how much it would cost to replace 1 12" by 12" window in a front door... how much the window would cost... I plan on fixing it myself... I really need the help to find out how much it would cost thanks... :(

We need a bit more info to help you. Is the window thermopane and what is the door made from wood, aluminum, fiberglass? http://www.glassiws.com/insulatedglass.htm This might help you with your numbers.