dmil is almost right. Most of his advice is very good, but Letter/Light Packet is not insured and seller's should be ready to add a few pennies to offset the very occasional loss or claim of loss.
US sellers of movies cannot* charge more than $4 including insurance to their customers. Canada Post will ship a 200 gram/2cm thick envelope to anywhere in the USA for $3.70.which allows us 30 cents for packaging and self-insurance.
*This is of course an over-simplification.
