it's not the sellers... it's the shipping providers.
US Postal Service, UPS, DHL, FedEx are all expensive for shipping outside the US boarders. I can only imagine it will get worse with the USPS's recent billion dollar operating loss, meaning they will increase their prices, which will mean other providers will follow.
it's odd that I can ship a 100lb engine around the country for about 50% more then I can send a 3.5lb manual to England for.