Created a new PriceRenderer class which is an extension of GtkCellRendererText for rendering Prices directly. We can get rid of the dispPrice stuff with this.
Actually made the new PriceRenderer work by removing the display price from the items store and make it applied to the Item Editor. Now to make it applied to the Order window...
Made the new PriceRenderer work on the Order screen by changing Order to store a raw Price value as well.