In the USA I use ebay's standard envelope when possible. My minumum charge for this is $2.00. Due to the restrictions on this service I may have to use First Class Package. My minimum charge for this service is $4.75. However, I do not charge for additional purchases that can ship in the same envelope. For example, buy one item for $2.00, or buy 10 items for the same $2.00 total.
For items shipped out of the USA my minimum charge is $3.50. Many small lots can usually be shipped with this $3.50. Larger items or many items will require additional postage. For large items I usually use eBays Intl Standard mail.
I have been a member of the American Philatelic Society since 1977 and try to make my descriptions accurate. Please let me know if I missed anything.