Some stats on the cost of shipping to get the juices flowing. These are from the book "Let My People Go Surfing" by Yvon Chouinard, founder of Patagonia and a personal hero.
"From raw materials it costs 110,000 BTUs to make a Patgonia shirt. Shipping it airfreight from Ventura, CA to a store in Boston costs 50,000 BTUs."
And generically, cost to ship per ton:
Rail or boat: 400 BTUs per ton per mile
Truck: 3,300 BTUs per ton per mile
Air cargo: 21,760 BTUs per ton per mile
So, whenever you can, take advantage of cheaper shipping methods. You'll save some money and do something for the environment as well!