Certain items have special pre-set shipping charges. Weight of the package will be taken into consideration and may add to the shipping charges. In some cases it will be faster. Overnight service is also based on when the order is placed. Orders taken late in the day may not be shipped out the same day.
Customer pays actual shipping charge.
I check the delivery companies web sites to find out the charge for overnight service. I do not add a service charge to this price. All packages to these destinations must go at least 2nd day service. Fedex and UPS require that these ship 2nd day. These charges are usually more then the regular 2nd day, so customer will pay actual charges.