Below are the shipping costs you can expect for the Avatar:
USA - $10-$20 via USPS
I give a range because it depends where in the country you live. If you're on the west coast it will be $20, East coast will be $10 and those in the middle of the country will be somewhere in between.
UK/EU/ROW - these will ship direct to backers from the manufacturer in the UK to keep the shipping cheaper and avoid many of the overseas charges and fees that get added when shipping from the US.
UK - £10
EU/ROW - £20
Shipping fees will be collected once the Kickstarter has ended when you fill out the pledge manager.