Yeah, I guess how much it weighs will also play a part on the price though and I think the shipping on the eBay Global Shipping Program is a bit more since the seller has to ship to item first to a company who will then forward the package internationally vs a direct shipment. Plus with a USPS direct shipment, most of the stuff I buy is expempt from customs charges.
USPS Priority and UPS Standard should be the cheapest but I'm not sure about FedEx. I heard Greyhound (the bus company) ships big and bulky stuff the cheapest but they don't ship across the border only Canada to Canada or US to US.